In English there is a difference between the adverb and the pronominal adverb.
I put it on it. / I put it thereon.
I put it on the table.
In English there is a difference between the adverb an the pronominal adverb. In Italian there is no difference between the adverb an the pronominal adverb.
Lo metto su. = I put it theron.
Lo metto sulla tavola. = I put it on the table.
Lo mettono su. => They put it thereon.
Stanno su. => They stand thereon.
Obviously in the last sentences su stands for something. If we don' t know on what they put it, the sentence is meaningless.
In Italian there is no difference either between the adverb and the preposition.
