The conjunctions perciò, per questo and pertanto describe the cause of something and correspond to the English conjunction therefore, hence. Normally they are considered adverbs or conjunctional adverbs. They have characteristics of an adverb because they are an adverbial adjunct which describes the cause of something and they have characteristics of a conjunction because they connect a main sentence to a subordinate clause. Nevertheless it would be better to call them pronominal conjunctions because actually they stand for something, for the idea expressed in the sentence before. In Italian it is even more suggestive to call them pronominal conjunctions because questo (per questo) and ciò (perciò) are pronouns. If a word is compound with a pronoun, it is quite logical that it has something of a pronoun. But the notion pronominal conjunction doesn' t exist. This kind of words are called conjunctional adverbs.

examples Aveva pochi soldi e perciò non poteva comprare il televisore.   He had little money and so he couldn' t buy a television.   Sono un operaio e per questo non mi ha degnato neanche di un saluto, cosa ne pensate?   I am a laboring man and so he not even dared to greet me, what do you think about it.   Questo sito pertanto non si rivolge a soggetti residenti in altri paesi.   This webiste is so not adressed to people who live in other countries.