Adverbs typically answer questions such as how?, in what way?, when?, where?, and to what extent?. This function is called the adverbial function, and is realised not just by single words (i.e., adverbs) but by adverbial phrases and adverbial clauses.
Adverbs are words like slowly, now, soon, and suddenly. An adverb usually modifies a verb or a verb phrase. It provides information about the manner, place, time, frequency, certainty, or other circumstances of the activity denoted by the verb or verb phrase. Examples:
1. The kids are skating together. (Here, the adverb together provides information about how the kids are skating.)
Adverbs can also modify adjectives and other adverbs.
1. You are quite right. (Here, the adverb quite modifies the adjective right.)
2. She spoke very loudly. (Here, the adverb very modifies another adverb – loudly.)
In English, adverbs of manner (answering the question how?) are often formed by adding -ly to adjectives (this, however, is not required e.x quick). Other languages often have similar methods for deriving adverbs from adjectives (French, for example, uses the suffix -ment), or else use the same form for both adjectives and adverbs. Some examples are listed under Adverbs in specific languages below.
Where the meaning permits, adverbs may undergo comparison, taking comparative and superlative forms. In English this is usually done by adding more and most before the adverb (more slowly, most slowly), although there are a few adverbs that take inflected forms, such as well, for which better and best are used.
Adverbs are considered a part of speech in traditional English grammar and are still included as a part of speech in grammar taught in schools and used in dictionaries. However, modern grammarians recognize that words traditionally grouped together as adverbs serve a number of different functions. Some would go so far as to call adverbs a "catch all" category that includes all words that do not belong to one of the other parts of speech.
A more logical approach to dividing words into classes relies on recognizing which words can be used in a certain context. For example, the only type of word that can be inserted in the following template to form a grammatical sentence is a noun:
The_____is red. (For example, "The hat is red".)
When this approach is taken, it is seen that adverbs fall into a number of different categories. For example, some adverbs can be used to modify an entire sentence, whereas others cannot. Even when a sentential adverb has other functions, the meaning is often not the same. For example, in the sentences She gave birth naturally and Naturally, she gave birth, the word naturally has different meanings. Naturally as a sentential adverb means something like "of course" and as a verb-modifying adverb means "in a natural manner". This "naturally" distinction demonstrates that the class of sentential adverbs is a closed class (there is resistance to adding new words to the class), whereas the class of adverbs that modify verbs isn't.
Words like very and particularly afford another useful example. We can say Perry is very fast, but not Perry very won the race. These words can modify adjectives but not verbs. On the other hand, there are words like here and there that cannot modify adjectives. We can say The sock looks good there but not It is a there beautiful sock. The fact that many adverbs can be used in more than one of these functions can confuse this issue, and it may seem like splitting hairs to say that a single adverb is really two or more words that serve different functions. However, this distinction can be useful, especially considering adverbs like naturally that have different meanings in their different functions. Huddleston distinguishes between a word and a lexicogrammatical-word.
Not is an interesting case. Grammarians have a difficult time categorizing it, and it probably belongs in its own class.
Adverbs in specific languages
Listed below are some of the principles for formation and use of adverbs in certain languages. For more information, see the articles on individual languages and their grammars.
In English adverbs can be formed from most adjectives with the ending -ly, and there are also many independent adverbs. For detailed information, see English grammar: Adverbs.
In Dutch adverbs have the basic form of their corresponding adjectives and are not inflected (except for comparison in which case they are inflected like adjectives, too).
In German the term adverb is differently defined than in the English language. German adverbs form a group of not inflectable words (except for comparison in which in rare cases some are inflected like adjectives, too). An English adverb, which is derived from an adjective, is arranged in the German language under the adjectives with adverbial use in the sentence. The others are also called adverbs in the German language.
In Scandinavian languages, adverbs are typically derived from adjectives by adding the suffix '-t', which makes it identical to the adjective's neuter form. Scandinavian adjectives, like English ones, are inflected in terms of comparison by adding '-ere'/'-are' (comparative) or '-est'/'-ast' (superlative). In inflected forms of adjectives the '-t' is absent. Periphrastic comparison is also possible.
In the Romanian language, the vast majority of adverbs are simply the masculine singular form of the corresponding adjective – one notable exception being bine ("well") / bun ("good"). However, there are some Romanian adverbs that are built from certain masculine singular nouns using the suffix "-ește", such as the following ones: băieț-ește (boyishly), tiner-ește (youthfully), bărbăt-ește (manly), frăț-ește (brotherly), etc.
Interlingua also forms adverbs by adding '-mente' to the adjective. If an adjective ends in c, the adverbial ending is '-amente'. A few short, invariable adverbs, such as ben, "well", and mal, "badly", are available and widely used.
In Esperanto, adverbs are not formed from adjectives but are made by adding '-e' directly to the word root. Thus, from bon are derived bone, "well", and bona, "good". See also: special Esperanto adverbs.
In Hungarian adverbs are formed from adjectives of any degree through the suffixes -ul/ül and -an/en depending on the adjective. E.g. szép (beautiful) -> szépen (beautifully) or the comparative szebb (more beautiful) -> szebben (more beautifully)
Modern Standard Arabic forms adverbs by adding the indefinite accusative ending '-an' to the root. For example, kathiir-, "many", becomes kathiiran "much". However, Arabic often avoids adverbs by using a cognate accusative plus an adjective.
Japanese forms adverbs from verbal adjectives by adding /ku/ (く) to the stem (e.g. haya- "rapid" hayai "quick/early", hayakatta "was quick", hayaku "quickly") and from nominal adjectives by placing /ni/ (に) after the adjective instead of the copula /na/ (な) or /no/ (の) (e.g. rippa "splendid", rippa ni "splendidly"). These derivations are quite productive but there are a few adjectives from which adverbs may not be derived.
In Portuguese, there is just one suffix used to create adverbs from adjectives "-mente", the same suffix is used in Interlingua, which is equivalent to English's "-ly".
In Modern Greek, an adverb is most commonly made by adding the endings <-α> and/or <-ως> to the root of an adjective. Often, the adverbs formed from a common root using each of these endings have slightly different meanings. So, <τέλειος> (<téleios>, meaning "perfect" and "complete") yields <τέλεια> (<téleia>, "perfectly") and <τελείως> (<teleíos>, "completely"). Not all adjectives can be transformed into adverbs by using both endings. <Γρήγορος> (<grígoros>, "rapid") becomes <γρήγορα> (<grígora>, "rapidly"), but not normally *<γρηγόρως> (*<grigóros>). When the <-ως> ending is used to transform an adjective whose tonal accent is on the third syllable from the end, such as <επίσημος> (<epísimos>, "official"), the corresponding adjective is accented on the second syllable from the end; compare <επίσημα> (<epísima>) and <επισήμως> (<episímos>), which both mean "officially". There are also other endings with particular and restricted use as <-ί>, <-εί>, <-ιστί>, etc. For example, <ατιμωρητί> (<atimorití>, "with impunity") and <ασυζητητί> (<asyzitití>, "indisputably"); <αυτολεξεί> (<autolexeí> "word for word") and <αυτοστιγμεί> (<autostigmeí>, "in no time"); <αγγλιστί> [<anglistí> "in English (language)"] and <παπαγαλιστί> (<papagalistí>, "by rote"); etc.
In Latvian, an adverb is formed from an adjective, by changing the masculine or feminine adjective endings -s and -a to -i. "Labs", meaning "good", becomes "labi" for "well". Latvian adverbs have a particular use in expressions meaning "to speak" or "to understand" a language. Rather than use the noun meaning "Latvian/English/Russian", the adverb formed form these words is used. "Es runāju latviski/angliski/krieviski" means "I speak Latvian/English/Russian", or very literally "I speak Latvianly/Englishly/Russianly". When a noun is required, the expression used means literally "language of the Latvians/English/Russians", "latviešu/angļu/krievu valoda".
In Russian, and analogously in Ukrainian and some other Slavic languages, most adverbs are formed by removing the adjectival suffices "-ий" "-а" or "-е" from an adjective, and replacing them with the adverbial "-о". For example, "швидкий", "гарна", and "смачне" (fast, nice, tasty) become "швидко", "гарно", and "смачно" (quickly, nicely, tastefully), similarly, "быстрый", "хороший" and "прекрасный" (quick, good, wonderful) become "быстро", "хорошо", "прекрасно" (quickly, well, wonderfully). Another wide group of adverbs are formed by gluing preposition to following oblique case form (now often dialectical or deprecated): з from+рідка the rare→зрідка rarely, на onto+долину bottom→надолину downwards. As well, note that adverbs are mostly placed before the verbs they modify: "Добрий син гарно співає." (A good son sings nicely/well). Although, there is no specific word order in East Slavic languages.
In Korean, adverbs are formed by replacing 다 of the dictionary form of a verb with 게. So, 쉽다 (easy) becomes 쉽게 (easily).
In Turkish, the same word usually serves as adjective and adverb: iyi bir kız ("a good girl"), iyi anlamak ("to understand well).
In Chinese, adverbs end in the word "地（的）", of which the English equivalent is "-ly".
In Persian, many adjectives serve as adverbs too (e.g. "خوب", "سریع", "تند") so there is no obvious way to recognize them out of context. The only exceptions are those Arabic adverbs with a "اً" suffix such as "ظاهراً" , واقعاً", etc.