Adverbs are normally considered something easy to define. Adverbs are words which specify another adverb, an adjective or a verb.
adverb specifying another adverb
He did it very well.
adverb specifying an adjective
He bought a very big house.
adverb specifying a verb
He speaks fast.
Adverbs are invariable, remains always the same. They can refere to something variable, but they are invariable themselves.
You speak loud.
He speaks loud.
That' s like that in most languages, but it must not be like that. In theory an adverb can be variable as well.
a => if the subject is in singular
He speaks louda.
an => if the subject is in plural
They speak loudan.
The problem is that this is not only theory, actually there are languages where the adverbs are variable, for instance czech. At the german version of the french course (www.franzoesisch-lehrbuch.de) we offered to pay 50 euros for everybody who knows a language where the adverbe is variable. That was not really a very good idea, because the website had been on the internet only four days when someone told us that in czech adverbs are variable and we had to pay 50 euros.
The second thing we have to see, if we are interested in pure theory, what is not the case because it is irrelevant concerning language learning, is the fact that the notion adverb refers to a function not to a type of word. What's the difference? Let's discuss the difference with a more obvious case. The word noun describes a type of word, apples, cars, trees, association are nouns. The word object refers to a function. The same noun, association in the examples below, can have different functions. It can be a direct object, an indirect object or subject.
direct object: He founded an association.
indirect object: He donated all his money to the association.
subject: The association buys a car.
That's in general the same thing with adjectives / adverbs. The same word can be an adverbe or an adjective.
They sing loud.
A loud noise anounced the arrival of the airplane.
From all that we can deduce that there is a problem concerning the terminology. Only in the case of words that can only be used as an adverb (very, too, less etc.) there is no difference between the type of word an its function. These words are always adverbs.
words which are always adverbs
She likes it very much.
Today we make a cake.
I go now.
adverb and adjective
adverb: The cars runs fast.
adjective: Fast cars consume a lot of fuel.
If we talk about adverbs in this chapter we are talking about words which can be used as adverbs. Better than the notion adverb is the notion adverbial adjunct. The adverbial adjunct is an ensemble of words which describes the temporal ("This night I go to the disco"), modal ("Mobilizing all his forces he was able to free himself"), causal ("Because of that we abandoned the project"), the final ("In order to see what' s going on, we went there") or the concessive ("Despite his handicap he is happy") circumstances of an action / event. The notions temporal, modal, causal, final and concessive we know already from the conjunctions.
But the adverbial conjunctions don't establish any relationship between two sentences.
Compare: a) Because of that we abandoned the project => No subordinate clause
b) He did dit it, because he wanted to do it => Subordinate clause (causal clause)
In the expamples above (a) this is quite obvious because there is no subordinate clause.
If you see it this way the adverb is a special case of the adverbial adjunct and the expression adverbial adjunct is clearer than the word adverb, because it refers to nothing but a function. The only way to justify the notion adverb is the fact that there are words which are nothing but adverbs. About the other strange words which are between preposition, conjunction and adverb we have already spoken in the chapter prepositions.
The problem mentioned above, the fact that nobody really knows to what the adverb refers to, to a function or a type of word, is less obvious in Italian because in most cases the adverb is different from the adjective. Like most romance languages Italian has a productive system which allows to form an adverb from any adjective. How this adverbs are formed we are going to see in the next chapters.