Consensus decision-making is a group decision-making process that seeks the consent of all participants. Consensus may be defined professionally as an acceptable resolution, one that can be supported, even if not the "favourite" of each individual. Consensus is defined by Merriam-Webster as, first, general agreement, and second, group solidarity of belief or sentiment. It has its origin in the Latin word cōnsēnsus (agreement), which is from cōnsentiō meaning literally feel together. It is used to describe both the decision and the process of reaching a decision. Consensus decision-making is thus concerned with the process of deliberating and finalizing a decision, and the social and political effects of using this process.
Alternative to common decision-making practices
Consensus decision-making is an alternative to commonly practised adversarial decision-making processes.Robert's Rules of Order, for instance, is a process used by many organizations. The goal of Robert’s Rules is to structure the debate and passage of proposals that win approval through majority vote. This process does not emphasize the goal of full agreement. Critics of Robert’s Rules believe that the process can involve adversarial debate and the formation of competing factions. These dynamics may harm group member relationships and undermine the ability of a group to cooperatively implement a contentious decision.
Consensus decision-making attempts to address the problems of both Robert’s Rules of Order and top-down models. Proponents claim that outcomes of the consensus process include:
Better Decisions: Through including the input of all stakeholders the resulting proposals may better address all potential concerns.
Better Implementation: A process that includes and respects all parties, and generates as much agreement as possible sets the stage for greater cooperation in implementing the resulting decisions.
Better Group Relationships: A cooperative, collaborative group atmosphere can foster greater group cohesion and interpersonal connection.
Perhaps the oldest example of consensus decision-making is the Iroquois Confederacy Grand Council, or Haudenosaunee, which has used consensus in decision-making using a 75% super majority to finalize decisions, potentially as early as 1142. Examples of consensus decision-making can likely be found among many indigenous peoples[who?], such as the African San.
Although the modern popularity of consensus decision-making in Western society dates from the women's liberation movement of the 1970s, and anti-nuclear movement the origins of formal consensus can be traced significantly further back.
The most notable of early Western consensus practitioners are the Religious Society of Friends, or Quakers, who adopted the technique as early as the 17th century. The Anabaptists, or Mennonites, too, have a history of using consensus decision-making and some believe Anabaptists practiced consensus as early as the Martyrs' Synod of 1527. Some Christians trace consensus decision-making back to the Bible. The Global Anabaptist Mennonite Encyclopedia references, in particular, Acts 15 as an example of consensus in the New Testament. The lack of legitimate consensus process in the unanimous conviction of Jesus by corrupt priests in an illegally held Sanhedrin court (which had rules preventing unanimous conviction in a hurried process) strongly influenced the views of pacifist Protestants, including the Anabaptists (Mennonites/Amish), Quakers and Shakers. In particular it influenced their distrust of expert-led courtrooms and to "be clear about process" and convene in a way that assures that "everyone must be heard" .
Unanimous consent (See agreement vs consent below)
Unanimous agreement minus one vote or two votes
Unanimous consent minus one vote or two votes
Super majority thresholds (90%, 80%, 75%, two-thirds, and 60% are common).
Executive committee decides
In groups that require unanimous agreement or consent (unanimity) to approve group decisions, if any participant objects, they can block consensus according to the guidelines described below. These groups use the term consensus to denote both the discussion process and the decision rule. Other groups use a consensus process to generate as much agreement as possible, but allow participants to finalize decisions with a decision rule that does not require unanimity. In this case, someone who has a 'block' or strong objection must live with the decision.
Agreement vs. consent
Giving consent does not necessarily mean that the proposal being considered is one’s first choice. Group members can vote their consent to a proposal because they choose to cooperate with the direction of the group, rather than insist on their personal preference. Sometimes the vote on a proposal is framed, “Is this proposal something you can live with?” This relaxed threshold for a yes vote can achieve full consent. This full consent, however, does not mean that everyone is in full agreement. Consent must be 'genuine and cannot be obtained by force, duress or fraud' 
Healthy consensus decision-making processes usually encourage and out dissent early, maximizing the chance of accommodating the views of all minorities. Since unanimity may be difficult to achieve, especially in large groups, or unanimity may be the result of coercion, fear, undue persuasive power or eloquence, inability to comprehend alternatives, or plain impatience with the process of debate, consensus decision-making bodies may use an alternative benchmark of consensus. These include the following:
Unanimity minus one (or U−1), requires all delegates but one to support the decision. The individual dissenter cannot block the decision although he or she may be able to prolong debate (e.g. via a filibuster). The dissenter may be the ongoing monitor of the implications of the decision, and their opinion of the outcome of the decision may be solicited at some future time. Betting markets in particular rely on the input of such lone dissenters. A lone bettor against the odds profits when his or her prediction of the outcomes proves better than that of the majority. This disciplines the market's odds.
Unanimity minus two (or U−2), does not permit two individual delegates to block a decision and tends to curtail debate with a lone dissenter more quickly. Dissenting pairs can present alternate views of what is wrong with the decision under consideration. Pairs of delegates can be empowered to find common ground that enables them to convince a third, decision-blocking, decision-maker to join them. If the pair can't convince a third party to join them, typically within a set time, their arguments are deemed unconvincing.
Unanimity minus three, (or U−3), and other such systems recognize the ability of four or more delegates to actively block a decision. U−3 and lesser degrees of unanimity are usually lumped in with statistical measures of agreement, such as: 80%, mean plus one sigma, two-thirds, or majority levels of agreement. Such measures usually do not fit within the definition of consensus.
Consensus blocking and other forms of dissent
Groups that require unanimity allow individual participants the option of blocking a group decision. This provision motivates a group to make sure that all group members consent to any new proposal before it is adopted. Proper guidelines for the use of this option, however, are important. The ethics of consensus decision-making encourage participants to place the good of the whole group above their own individual preferences. When there is potential for a block to a group decision, both the group and dissenters in the group are encouraged to collaborate until agreement can be reached. Simply vetoing a decision is not considered a responsible use of consensus blocking. Some common guidelines for the use of consensus blocking include:
Limiting the option to block consensus to issues that are fundamental to the group’s mission or potentially disastrous to the group.
Providing an option for those who do not support a proposal to “stand aside” rather than block.
Requiring a block from two or more people to put a proposal aside.
Requiring the blocking party to supply an alternative proposal or a process for generating one.
Limiting each person’s option to block consensus to a handful of times in one’s life.
When a participant does not support a proposal, he or she does not necessarily need to block it. When a call for consensus on a motion is made, a dissenting delegate has one of three options:
Declare reservations: Group members who are willing to let a motion pass but desire to register their concerns with the group may choose "declare reservations." If there are significant reservations about a motion, the decision-making body may choose to modify or re-word the proposal.
Stand aside: A "stand aside" may be registered by a group member who has a "serious personal disagreement" with a proposal, but is willing to let the motion pass. Although stand asides do not halt a motion, it is often regarded as a strong "nay vote" and the concerns of group members standing aside are usually addressed by modifications to the proposal. Stand asides may also be registered by users who feel they are incapable of adequately understanding or participating in the proposal.
Block: Any group member may "block" a proposal. In most models, a single block is sufficient to stop a proposal, although some measures of consensus may require more than one block (see previous section, Decision rules).
Blocks are generally considered an extreme measure—only used when a member feels a proposal endangers the organization or its participants, or violates the mission of the organization (i.e., a principled objection). In some consensus models, a group member opposing a proposal must work with its proponents to find a solution that works for everyone.
There are multiple stepwise models of how to make decisions by consensus. They vary in the amount of detail the steps describe. They also vary depending on how decisions are finalized. The basic model involves
collaboratively generating a proposal,
identifying unsatisfied concerns, and then
modifying the proposal to generate as much agreement as possible.
After a concerted attempt at generating full agreement, the group can then apply its final decision rule to determine if the existing level of agreement is sufficient to finalize a decision.
Consensus decision-making with consensus blocking
Flowchart of basic consensus decision-making process.
Groups that require unanimity commonly use a core set of procedures depicted in this flow chart.
Once an agenda for discussion has been set and, optionally, the ground rules for the meeting have been agreed upon, each item of the agenda is addressed in turn. Typically, each decision arising from an agenda item follows through a simple structure:
Discussion of the item: The item is discussed with the goal of identifying opinions and information on the topic at hand. The general direction of the group and potential proposals for action are often identified during the discussion.
Formation of a proposal: Based on the discussion a formal decision proposal on the issue is presented to the group.
Call for consensus: The facilitator of the decision-making body calls for consensus on the proposal. Each member of the group usually must actively state their agreement with the proposal, often by using a hand gesture or raising a colored card, to avoid the group interpreting silence or inaction as agreement. The number of blocks is counted to determine if this step's consent threshold is satisfied. If it is, dissenters are asked to collaborate on a minority position or statement so that any unique or shared concerns with proceeding with the agreement, or any harms, can be addressed/minimized. This can happen even if the consent threshold is unanimity, especially if many voters stand aside.
Identification and addressing of concerns: If consensus is not achieved, each dissenter presents his or her concerns on the proposal, potentially starting another round of discussion to address or clarify the concern.
Modification of the proposal: The proposal is amended, re-phrased or ridered in an attempt to address the concerns of the decision-makers. The process then returns to the call for consensus and the cycle is repeated until a satisfactory decision passes the consent threshold for the group.
Quaker-based consensus is effective because it puts in place a simple, time-tested structure that moves a group towards unity. The Quaker model has been employed in a variety of secular settings. The process allows hearing individual voices while providing a mechanism for dealing with disagreements.
The following aspects of the Quaker model can be effectively applied in any consensus decision-making process, and is an adaptation prepared by Earlham College:
Multiple concerns and information are shared until the sense of the group is clear.
Key components of Quaker-based consensus include a belief in a common humanity and the ability to decide together. The goal is "unity, not unanimity." Ensuring that group members speak only once until others are heard encourages a diversity of thought. The facilitator is understood as serving the group rather than acting as person-in-charge. In the Quaker model, as with other consensus decision-making processes, by articulating the emerging consensus, members can be clear on the decision, and, as their views have been taken into account, are likely to support it.
Modern Large-Group Quaker Processes
FUM/FGC Friends conduct business in yearly meetings of perhaps 100 to 500 participants. Over the last three centuries they have evolved a number of practices peculiar to their aims. The following practices are traditional in both New York Yearly Meeting and in New England Yearly Meeting:
A typical yearly meeting session has a presiding clerk, one or two recording clerks and a reading clerk on stage. Partitioning the work load with extra clerks lowers the stress level on the presiding clerk.
Business sessions start with a period of corporate silent worship.
A period of silent worship, perhaps thirty seconds, is allotted by the presiding clerk after each person speaks. This slows the pace of the business meeting down and allows people to contemplate people's messages.
The use of wireless microphones helps to slow down the pace of the meeting. Volunteer microphone runners are instructed to walk at a reasonably slow pace toward someone standing and waiting to be recognized.
The clerk often recognizes who speaks first, then second, then third.
A pastoral care team upholds the presiding clerk, or simply the clerk, in prayer.
Attempts are made to take minor editing functions off of the floor of the meeting. Minutes are polished by a committee before presenting them on the meeting floor. All suggested small corrections are incorporated either on the spot by the caucusing clerks, or at a special impromptu meeting after the current business session ends. Corrected minutes are then brought back onto the floor of the meeting at a later date.
Major, complex concerns result in a called threshing session, a meeting of people most concerned about the issue.
New England Yearly Meeting has discovered the benefits of anchor groups, groups of about ten participants who meet every day during a multi-day yearly meeting. People sometimes need to vocalize their personal opinions on issues to a few other people, in part because people think aloud.
Every 20 or 30 years, each yearly meeting's consensus practices are re-codified in a new edition of that yearly meeting's Faith and Practice book.
The Consensus-Oriented Decision-Making model offers a detailed step-wise description of consensus process. It can be used with any type of decision rule. It outlines the process of how proposals can be collaboratively built with full participation of all stakeholders. This model lets groups be flexible enough to make decisions when they need to, while still following a format based on the primary values of consensus decision-making. The CODM steps include:
Framing the topic
Identifying Underlying Concerns
Collaborative Proposal Building
Choosing a Direction
Synthesizing a Final Proposal
Overlaps with deliberative methods
Consensus decision-making models overlap significantly with deliberative methods, which are processes for structuring discussion that may or may not be a lead-in to a decision.
The consensus decision-making process often has several roles designed to make the process run more effectively. Although the name and nature of these roles varies from group to group, the most common are the facilitator, a timekeeper, an empath and a secretary or notes taker. Not all decision-making bodies use all of these roles, although the facilitator position is almost always filled, and some groups use supplementary roles, such as a Devil's advocate or greeter. Some decision-making bodies opt to rotate these roles through the group members in order to build the experience and skills of the participants, and prevent any perceived concentration of power.
The common roles in a consensus meeting are:
Facilitator: As the name implies, the role of the facilitator is to help make the process of reaching a consensus decision easier. Facilitators accept responsibility for moving through the agenda on time; ensuring the group adheres to the mutually agreed-upon mechanics of the consensus process; and, if necessary, suggesting alternate or additional discussion or decision-making techniques, such as go-arounds, break-out groups or role-playing. Some consensus groups use two co-facilitators. Shared facilitation is often adopted to diffuse the perceived power of the facilitator and create a system whereby a co-facilitator can pass off facilitation duties if he or she becomes more personally engaged in a debate.
Timekeeper: The purpose of the timekeeper is to ensure the decision-making body keeps to the schedule set in the agenda. Effective timekeepers use a variety of techniques to ensure the meeting runs on time including: giving frequent time updates, ample warning of short time, and keeping individual speakers from taking an excessive amount of time.
Empath or 'Vibe Watch': The empath, or 'vibe watch' as the position is sometimes called, is charged with monitoring the 'emotional climate' of the meeting, taking note of the body language and other non-verbal cues of the participants. Defusing potential emotional conflicts, maintaining a climate free of intimidation and being aware of potentially destructive power dynamics, such as sexism or racism within the decision-making body, are the primary responsibilities of the empath.
Note taker: The role of the notes taker or secretary is to document the decisions, discussion and action points of the decision-making body.
Tools and methods
Non-verbal means of expression can also reduce contention or keep issues from spreading out in time across an entire meeting. Various methods of agenda control exist, mostly relying on an explicit chairperson with the power to interrupt off-topic or rambling discourse. This gets more difficult if there is no such chair and accordingly the attitude of the entire group must be assessed by each speaker. Verbal interruptions inevitably become common, possibly in the form of grumbling, muttering, and eventually sharp words, if there is no effective means of cutting off persons making false factual statements or rambling off a topic.
The Levi Hand Signal Technique (LHST) employed by Otesha  "allows meeting participants to register their intent to make two distinct kinds of comments: those that are directly in response to someone else's comment ('reactive comments') and those that are separate thoughts ('unique comments'). Intent to register a reactive comment is signalled by a different hand signal than is intent to register a unique comment. We used an index finger for the former and a full hand for the latter." This clears direct responses to a contentious comment faster—and makes it harder to insert it in a long speakers' list and count on a long delay between the utterance and the challenge to create the appearance of agreement.
"Twinkling fingers", similarly, is a nonverbal way of expressing strong agreement, similar to applause but without the interruption and possibly less intimidation of disagreement than applause or cheers can create . The Occupy movement has used these methods.
Closely related are the human microphone methods, which make a large group less reliant on amplification or other technologies, and may require people to exactly repeat or "amplify" comments they may not agree with, so others can hear. Amplifiers are banned in many public places without permits, so this method allows a group to literally 'occupy' a location it would otherwise not be able to meet in. Effectively, the verbal capacity of the people attending is marshalled to amplify one person at a time, with the understanding that any person in the crowd with anything to say would receive a similar courtesy.
For more detail on these methods and their use in specific processes see the section Hand Signals below.
Functional Consensus Flowchart
What is often wanting/missing in consensus discussions is a means of efficiently moving through the process. A blueprint to powerfully overcome the logistical and social challenges of consensus decisions, making it practical, efficient, and effective in today’s world, is depicted in the consensus flowchart "Game of Consensus."
Some consensus decision-making bodies use a system of colored cards to speed up and ease the consensus process. Most often, each member is given a set of three colored cards: red, yellow and green. The cards can be raised during the process to indicate the member's input. Cards can be used during the discussion phase as well as during a call for consensus. The cards have different meanings depending on the phase in which they are used. The meaning of the colors are:
Red: During discussion, a red card is used to indicate a point of process or a breach of the agreed upon procedures. Identifying offtopic discussions, speakers going over allowed time limits or other breaks in the process are uses for the red card. During a call for consensus, the red card indicates the member's opposition (usually a "principled objection") to the proposal at hand. When a member, or members, use a red card, it becomes their responsibility to work with the proposing committee to come up with a solution that works for everyone.
Yellow: In the discussion phase, the yellow card is used to indicate a member's ability to clarify a point being discussed or answer a question being posed. Yellow is used during a call for consensus to register a stand aside to the proposal or to formally state any reservations.
Green: A group member can use a green card during discussion to be added to the speakers list. During a call for consensus, the green card indicates consent.
Some decision-making bodies use a modified version of the colored card system with additional colors, such as orange to indicate a non-blocking reservation stronger than a stand-aside.
Hand signals are often used by consensus decision-making bodies as a way for group members to nonverbally indicate their opinions or positions. They have been found useful in facilitating groups of 6 to 250 people. They are particularly useful when the group is multi-lingual.
The nature and meaning of individual gestures varies from group to group. Nonetheless, there is a widely adopted core set of hand signals. These include: wiggling of the fingers on both hands, a gesture sometimes referred to as "twinkling", to indicate agreement; raising a fist or crossing both forearms with hands in fists to indicate a block or strong disagreement; and making a "T" shape with both hands, the "time out" gesture, to call attention to a point of process or order. One common set of hand signals is called the "Fist-to-Five" or "Fist-of-Five". In this method each member of the group can hold up a fist to indicate blocking consensus, one finger to suggest changes, two fingers to discuss minor issues, three fingers to indicate willingness to let issue pass without further discussion, four fingers to affirm the decision as a good idea, and five fingers to volunteer to take a lead in implementing the decision.A similar set of hand signals are used by the Occupy Wall Street protesters in their group negotiations.
Another common set of hand signals used is the "Thumbs" method, where Thumbs Up = agreement; Thumbs Sideways = have concerns but won't block consensus; and Thumbs Down = I don't agree and I won't accept this proposal. This method is also useful for "straw polls" to take a quick reading of the group's overall sentiment for the active proposal.
A slightly more detailed variation on the thumbs proposal can be used to indicate a 5-point range: (1) Thumb-up = strongly agree, (2) Palm-up = mostly agree, (3) Thumb Sideways = "on the fence" or divided feelings, (4) Palm down = mostly disagree, and (5) Thumb down = strongly disagree.
Other useful hand signs include:
Clarifying Question - using your hand to form a "C" shape to indicate that you have a clarifying question, often this hand sign means that a person is invited to ask their question before a vote is taken.
Point of Information - pointing your index finger upwards to indicate that you have some important factual information that relates to the discussion or decision at hand.
Process Point - forming a triangle with your hands or hands and arms to indicate that you have an important concern with the meeting or decision-making process.
Completed Dotmocracy sheet
Dotmocracy sheets are designed to complement a consensus decision-making process by providing a simple way to visibly document levels of agreement among participants on a large variety of ideas.
Participants write down ideas on paper forms called Dotmocracy sheets and fill in one dot per sheet to record their opinion of each idea on a scale of “strong agreement”, “agreement”, “neutral”, “disagreement”, “strong disagreement” or “confusion”. Participants sign each sheet they dot and may add brief comments. The result is a graph-like visual representation of the group's collective opinions on each idea.
The Step-by-Step Process and Rules defined in the Dotmocracy Handbook reinforce consensus decision-making by promoting equal opportunity, open discussion, the drafting of many proposals, the identification of concerns and the encouragement of idea modification.
Sometimes some common form of voting such as First-past-the-post is used as a fall-back method when consensus cannot be reached within a given time frame. However, if the potential outcome of the fall-back method can be anticipated, then those who support that outcome have incentives to block consensus so that the fall-back method gets applied. Special fall-back methods have been developed that reduce this incentive.
Specific Applications of Consensus
Japanese companies normally use consensus decision-making, meaning that everyone in the company is consulted on each decision. A ringi-sho is a circulation document used to obtain agreement. It must first be signed by the lowest level manager, and then upwards, and may need to be revised and the process started over.
One tradition in support of rough consensus is the tradition of humming rather than (countable) hand-raising; this allows a group to quickly tell the difference between "one or two objectors" or a "sharply divided community", without making it easy to slip into "majority rule".
Much of the business of the IETF is carried out on mailing lists, where all parties can speak their view at all times.
Decision Making in Psychology and Counseling: The Social Constructivism Model
In 2001, Robert Rocco Cottone published a consensus-based model of professional decision-making for counselors and psychologists. Based on social constructivist philosophy, the model operates as a consensus-building model, as the clinician addresses ethical conflicts through a process of negotiating to consensus. Conflicts are resolved by consensually agreed on arbitrators who are defined early in the negotiation process.
BLM Collaborative Stakeholder Engagement
The United States Bureau of Land Management's policy is to seek to use collaborative stakeholder engagement as standard operating practice for natural resources projects, plans, and decision-making except under unusual conditions such as when constrained by law, regulation, or other mandates or when conventional processes are important for establishing new, or reaffirming existing, precedent.
The ISO process for adopting new standards is called consensus-based decision-making, In the ISO system consensus is defined as
General agreement, characterized by the absence of sustained opposition to substantial issues by any important part of the concerned interests and by a process that involves seeking to take into account the views of all parties concerned and to reconcile any conflicting arguments.
Where decision-making is subject to ballot by member bodies, a requirement for super-majority support generally applies.
During the ISO Standardization Process, if a Draft Internation al Standard does not receive 75% of the vote, it is not approved, returning to lower stages.
Critics of consensus blocking often observe that the option, while potentially effective for small groups of motivated or trained individuals with a sufficiently high degree of affinity, has a number of possible shortcomings, notably
Preservation of the Status quo: In decision-making bodies that use formal consensus, the ability of individuals or small minorities to block agreement gives an enormous advantage to anyone who supports the existing state of affairs. This can mean that a specific state of affairs can continue to exist in an organization long after a majority of members would like it to change. The incentive to block can however be removed by using a special kind of voting process.
Susceptibility to widespread disagreement: Giving the right to block proposals to all group members may result in the group becoming hostage to an inflexible minority or individual. When a popular proposal is blocked the group actually experiences widespread disagreement, the opposite of the consensus process's goal. Furthermore, "opposing such obstructive behavior [can be] construed as an attack on freedom of speech and in turn [harden] resolve on the part of the individual to defend his or her position." As a result, consensus decision-making has the potential to reward the least accommodating group members while punishing the most accommodating.
Consensus is not Groupthink
Consensus seeks to improve solidarity in the long run. Accordingly it should not be confused with unanimity in the immediate situation, which is often a symptom of groupthink. Studies of effective consensus process usually indicate a shunning of unanimity or "illusion of unanimity" that does not hold up as a group comes under real world pressure (when dissent reappears). Cory Doctorow, Ralph Nader and other proponents of deliberative democracy or judicial-like methods view the explicit dissent as a symbol of strength. Lawrence Lessig considers it a major strength of working projects like public wikis. Schutt, Starhawk and other practitioners of direct action focus on the hazards of apparent agreement followed by action in which group splits become dangerously obvious.
Whatever one thinks of the merits of seeking a unanimous agreement in a particular situation, in general unanimous, or apparently unanimous, decisions have numerous drawbacks. They may be symptoms of a systemic bias, a rigged process (where an agenda is not published in advance or changed when it becomes clear who is present to consent), fear of speaking one's mind, a lack of creativity (to suggest alternatives) or even a lack of courage (to go further along the same road to a more extreme solution that would not achieve unanimous consent).
Unanimity is achieved when the full group apparently consents to a decision. It has disadvantages insofar as further disagreement, improvements or better ideas then remain hidden, but effectively ends the debate moving it to an implementation phase. Some consider all unanimity a form of groupthink, and some experts  propose "coding systems...for detecting the illusion of unanimity symptom." In Consensus is not Unanimity, consensus practitioner and activist leader Starhawk wrote:
Many people think of consensus as simply an extended voting method in which every one must cast their votes the same way. Since unanimity of this kind only rarely occurs in groups with more than one member, groups that try to use this kind of process usually end up being either extremely frustrated or coercive. Either decisions are never made (leading to the demise of the group, its conversion into a social group that does not accomplish any tasks), they are made covertly, or some group or individual dominates the rest. Sometimes a majority dominates, sometimes a minority, sometimes an individual who employs "the block". But no matter how it is done, it is NOT consensus.
Confusion between unanimity and consensus, in other words, usually causes consensus decision-making to fail, and the group then either reverts to majority or supermajority rule or disbands.
Most robust models of consensus exclude uniformly unanimous decisions and require at least documentation of minority concerns. Some state clearly that unanimity is not consensus but rather evidence of intimidation, lack of imagination, lack of courage, failure to include all voices, or deliberate exclusion of the contrary views.
The most famous unanimous decision in the Western canon illustrates all those failures; New Testament historian Elaine Pagels cites the Sanhedrin's unanimous vote to convict Jesus of Nazareth. To a Jewish audience familiar with that court's requirement to set free any person unanimously convicted as not having a proper defense, Pagels proposes that the story is intended to signal the injustice of unanimous rush to agreement and Jesus' lack of a defender. She cites the shift away from this view and towards preference for visible unanimity as a factor in later "demonization" of Jews, pagans, heretics (notably Gnostics) and others who disagreed with orthodox views in later Christianity. Unanimity, in other words, became a priority where it had been an anathema.
Some formal models based on graph theory attempt to explore the implications of suppressed dissent and subsequent sabotage of the group as it takes action 
Extremely high-stakes decision-making, such as judicial decisions of appeals courts, always require some such explicit documentation. Consent however is still observed that defies factional explanations. Nearly 40% of Supreme Court of US decisions, for example, are unanimous, though often for widely varying reasons. "Consensus in Supreme Court voting, particularly the extreme consensus of unanimity, has often puzzled Court observers who adhere to ideological accounts of judicial decision making." . Historical evidence is mixed on whether particular Justices' views were suppressed in favour of public unity. 
Another method to achieve more agreement to satisfy a strict threshold a voting process under which all members of the group have a strategic incentive to agree rather than block. However, this makes it very difficult to tell the difference between those who support the decision and those who merely tactically tolerate it for the incentive. Once they receive that incentive, they may undermine or refuse to implement the agreement in various and non-obvious ways. In general voting systems avoid allowing offering incentives (or "bribes") to change a heartfelt vote.
Abilene paradox: Consensus decision-making is susceptible to all forms of groupthink, the most dramatic being the Abilene paradox. In the Abilene paradox, a group can unanimously agree on a course of action that no individual member of the group desires because no one individual is willing to go against the perceived will of the decision-making body.
Time Consuming: Since consensus decision-making focuses on discussion and seeks the input of all participants, it can be a time-consuming process. This is a potential liability in situations where decisions must be made speedily, or where it is not possible to canvass opinions of all delegates in a reasonable time. Additionally, the time commitment required to engage in the consensus decision-making process can sometimes act as a barrier to participation for individuals unable or unwilling to make the commitment. However, once a decision has been reached it can be acted on more quickly than a decision handed down. American businessmen complained that in negotiations with a Japanese company, they had to discuss the idea with everyone even the janitor, yet once a decision was made the Americans found the Japanese were able to act much quicker because everyone was on board, while the Americans had to struggle with internal opposition.
Majority voting processes
Proponents of consensus decision-making view procedures that use majority rule as undesirable for several reasons. Majority voting is regarded as competitive, rather than cooperative, framing decision-making in a win/lose dichotomy that ignores the possibility of compromise or other mutually beneficial solutions. Carlos Santiago Nino, on the other hand, has argued that majority rule leads to better deliberation practice than the alternatives, because it requires each member of the group to make arguments that appeal to at least half the participants. A. Lijphart reaches the same conclusion about majority rule, noting that majority rule encourages coalition-building. Additionally, opponents of majority rule claim that it can lead to a 'tyranny of the majority', a scenario in which a majority places its interests so far above those of an individual or minority group as to constitute active oppression. Some voting theorists, however, argue that majority rule may actually prevent tyranny of the majority, in part because it maximizes the potential for a minority to form a coalition that can overturn an unsatisfactory decision.
Advocates of consensus would assert that a majority decision reduces the commitment of each individual decision-maker to the decision. Members of a minority position may feel less commitment to a majority decision, and even majority voters who may have taken their positions along party or bloc lines may have a sense of reduced responsibility for the ultimate decision. The result of this reduced commitment, according to many consensus proponents, is potentially less willingness to defend or act upon the decision.
^Ralph A Lebold (1989). "Consensus". Global Anabaptist Mennonite Encyclopedia Online. Global Anabaptist Mennonite Encyclopedia Online. Archived from the original on March 13, 2007. Retrieved 2007-01-17.
^Tomalin, Barry; Knicks, Mike (2008). "Consensus or individually driven decision-". The World's Business Cultures and How to Unlock Them. Thorogood Publishing,. p. 109. ISBN978-1-85418-369-9.|accessdate= requires |url= (help)