Adverbs are traditionally regarded as one of the parts of speech. However, modern linguists note that it has come to be used as a kind of "catch-all" category, used to classify words with various different types of syntactic behavior, not necessarily having much in common except that they do not fit into any of the other available categories (noun, adjective, preposition, etc.)
The English word adverb derives (through French) from Latin adverbium, from ad- ("to"), verbum ("word", "verb"), and the nominal suffix -ium. The term implies that the principal function of adverbs is to act as modifiers of verbs or verb phrases. An adverb used in this way may provide information about the manner, place, time, frequency, certainty, or other circumstances of the activity denoted by the verb or verb phrase. Some examples:
She sang loudly (loudly modifies the verb sang, indicating the manner of singing)
We left it here (here modifies the verb phrase left it, indicating place)
I worked yesterday (yesterday modifies the verb worked, indicating time)
You often make mistakes (often modifies the verb phrase make mistakes, indicating frequency)
He undoubtedly did it (undoubtedly modifies the verb phrase did it, indicating certainty)
Another way of describing a noun or verb.
Adverbs can also be used as modifiers of adjectives, and of other adverbs, often to indicate degree. Examples:
You are quite right (the adverb quite modifies the adjective right)
She sang very loudly (the adverb very modifies another adverb – loudly)
They can also modify noun phrases, prepositional phrases, or whole clauses or sentences, as in the following examples:
I bought only the fruit (only modifies the noun phrase the fruit)
She drove us almost to the station (almost modifies the prepositional phrase to the station)
Certainly we need to act (certainly modifies the sentence as a whole)
Adverbs are thus seen to perform a wide range of modifying functions. The major exception is the function of modifier of nouns, which is performed instead by adjectives (compare she sang loudly with her loud singing disturbed me; here the verb sang is modified by the adverb loudly, whereas the noun singing is modified by the adjective loud). However, as seen above, adverbs may modify noun phrases, and so the two functions may sometimes be superficially very similar:
Even camels need to drink
Even numbers are divisible by two
The word even in the first sentence is an adverb, since it is an "external" modifier, modifying camels as a noun phrase (compare even these camels ...), whereas the word even in the second sentence is an adjective, since it is an "internal" modifier, modifying numbers as a noun (compare these even numbers ...). It is nonetheless possible for certain adverbs to modify a noun; in English the adverb follows the noun in such cases, as in:
The people here are friendly
The show features dances galore
There is a shortage internationally of protein for animal feeds
Adverbs can sometimes be used as predicative expressions; in English this applies especially to adverbs of location:
Your seat is there.
When the function of an adverb is performed by an expression consisting of more than one word, it is called an adverbial phrase or adverbial clause, or simply an adverbial.
In English, adverbs of manner (answering the question how?) are often formed by adding -ly to adjectives. 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. Many other adverbs, however, are not related to adjectives in this way; they may be derived from other words or phrases, or may be single morphemes. Examples of such adverbs in English include here, there, together, yesterday, aboard, very, almost, etc.
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.
For more information about the formation and use of adverbs in English, see English grammar § Adverbs. For other languages, see § In specific languages below, and the articles on individual languages and their grammars.
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 describe adverbs a "catch-all" category that includes all words that do not belong to one of the other parts of speech.
A 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: in the first sentence, as a verb-modifying adverb, it means "in a natural manner", while in the second sentence, as a sentential adverb, it means something like "of course".
Words like very afford another 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 the 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 when considering adverbs like naturally that have different meanings in their different functions. Rodney Huddleston distinguishes between a word and a lexicogrammatical-word.
Grammarians find difficulty categorizing negating words, such as the English not. Although traditionally listed as an adverb, this word does not behave grammatically like any other, and it probably should be placed in a class of its own.