A correspondent sends in the following passage from the Times (30 July): 'In Adam Sage’s article about Dominique Strauss-Kahn (July 23) he says that Triston Banon’s mother "convinced her not to make a formal complaint". No, she didn’t: she persuaded her. You convince someone of the truth of something, but you persuade them to take a course of action. ... It is a classic example of a new construction that is acceptable or at least unexceptionable to some and repugnant to others.' And he adds, a mite confused: Can I tell my students it's OK to use convince to do something?
This is purely a grammatical issue. There's no problem when these verbs are used with a following that construction. There is a difference in meaning, but that is a different point. Compare:
(1) I persuaded John that he should go to the cinema.
(2) I convinced John that he should go to the cinema.
In (1), the focus is on the process of argument; it's a step anticipating a successful conclusion. In (2) the focus is on the result; the conclusion has been successfully achieved. In this pair of examples, the nuance is inconsequential; but in (3) and (4) a contrast is drawn:
(3) I persuaded him to go, but he wasn't convinced it was the right thing to do.
(4) I found his argument persuasive but not convincing.
The lack of synonymy is illustrated by the impossibility of reversing the verbs:
(5) I convinced him to go, but he wasn't persuaded it was the right thing to do.
(6) I found his argument convincing but not persuasive.
In some cases, the context motivates the stronger interpretation, as in (7):
(7) He convinced (?persuaded) the police that he was innocent.
However, these examples are few compared with the many contexts in which either verb could substitute for the other without anyone noticing, as in (8):
(8) I persuaded/convinced John that it would be wise to leave early.
Persuade has long (since the Middle Ages) been used with the nonfinite construction:
(9) I persuaded John to go to the cinema.
The infinitive brings a different semantic implication: the focus is on the action rather than on the mental state. And given the overlap in meaning, it was only a matter of time for this construction to be extended to convince. The surprising thing is that this didn't happen until the 1950s. First recorded usages are in the USA:
(10) I convinced John to go to the cinema.
This brought the usual complaints from the prophets of linguistic doom, but the rapid growth in popularity of the usage quickly led to it being recognized in dictionaries and grammars in both British and American English. The OED, for example, notes it without comment. The that construction is still the more frequent one, especially in British English, but the greater succinctness of the to construction - one word instead of three - has probably been a factor in its growth.
So, in short, I would certainly let students use both constructions with convince, but warn them that some people still find the to form uncomfortable. In such circumstances, when one never knows who will be reading what one writes, it is always wise to be conservative. One doesn't want one's application for a job to be rejected by a potential employer who is still living in the linguistic past, and who finds this usage - as the Times writer says - repugnant.