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Argument from authority (argumentum ad verecundiam), also authoritative argument and appeal to authority, is a special type of inductive-reasoning argument that usually is presented in the form of a statistical syllogism, which argues the case from the general to the specific. Although certain classes of argument from authority can constitute strong inductive arguments, the appeal to authority usually is applied fallaciously, either the Authority is not a subject-matter expert, or there is no consensus among experts in the subject matter, or both.
The argument from authority (argumentum ad verecundiam) can take several forms. As a statistical syllogism, the argument has the following basic structure: 
The two factors — legitimate expertise and expert consensus — can be incorporated to the structure of the statistical syllogism, in which case, the argument from authority can be structured thus: 
Fallacious arguments from authority often are the result of failing to meet at least one of the required two conditions (legitimate expertise and expert consensus) structurally required in the forms of a statistical syllogism. First, when the inference fails to meet the first condition (inexpert authority), it is an appeal to inappropriate authority, which occurs when an inference relies upon a person or a group without relevant expertise or knowledge of the subject matter under discussion.
Second, because the argument from authority is an inductive-reasoning argument — wherein is implied that the truth of the conclusion cannot be guaranteed by the truth of the premises — it also is fallacious to assert that the conclusion must be true. Such a determinative assertion is a logical non sequitur, because, although the inductive argument might have merit — either probabilistic or statistical — the conclusion does not follow unconditionally, in the sense of being logically necessary.
When there is significant disagreement among experts, the resolution to the disagreement can include authoritative arguments, as in psychiatry and economics, which are fields of intellectual enquiry wherein legitimate experts continually contradict each other in disputation, and cannot all be correct and in the right. Therefore, before accepting an “expert opinion” a person must ask: “Do the experts in this subject agree about this specific issue?”  In the case of religion, there usually are theologians and clerics who have spent their lives studying the theology of a denomination or of a sect of Christianity, or Islam, or Judaism et al. Despite such diversity of theologic perspectives, such experts disagree about the particulars of their deities and of revealed Truth.
As in the psychology of the layman, bias and prejudice are human weaknesses common to legitimate experts, and their authority. Thus, wishful thinking is a mental misdemeanour possible in the practise of authoritative argument, because an authority, a man or a woman who invested much time and effort to becoming a legitimate expert in the subject matter of a field of intellectual enquiry, naturally would want to be the correct party in a subject-matter disputation. In professional praxis, evidence that a legitimate expert is either biased or prejudiced, or both, weakens that person's arguments and expert opinion. Moreover, such partiality also can apply to rebut the arguments presented, either in advocacy or in defence of a statistical syllogism. The nature of human psychology moots any intuitive certainty about whether or not a legitimate expert (who might or might not be biased or prejudiced, or both) has dispassionately considered and evaluated the arguments presented in the statistical syllogism; or if the authority of the proffered expert opinion is tainted with bias and with prejudice. Hence, the medical authority of physicians employed by tobacco companies is necessarily dubious and unreliable, because of their partiality to the business interests of the employer company.
Salmon, M. H. (2006). Introduction to Logic and Critical Thinking. Mason, OH: Thomson Wadsworth. pp. 118–9.