1. The verbals express the idea of action( to write, writing, written, writing: There are a lot of things to marvel at but, first, a lot of questions to ask. A man to see you! S.Plath).
2. They all have the categories of correlation and voice, the infinitive has one more verbal category, that of aspect (to be writing, to have written, to be written, to have been written, to have been writing; being written, having written, having been written). The distinction between the active and the passive, the non-perfect and perfect forms can be neutralized in the non-finites (The house is to let àThe house is to be let; I am awfully surprised to find you here à I am awfully surprised to have found you here The book isn’t worth buying àThe book isn’t worth being bought. Your stomach wants educating àYour stomach wants being educated. Arriving there he immediately understood everything à Having arrived there he immediately understood everything).
3. The non-finites, like the finites, are seldom used singly, without complements (Marriage is not a hopeless affair doomed to failure. He seems to have done it).