What's the difference in usage between suasive and persuasive? I just read the former used, here on this StackExchange, where the latter would have worked perfectly, IMO. Is there a subtle distinction between the two words? Can anyone give me an example where using suasive would be compellingly better than using persuasive? And finally, as I'd never seen the word suasive before today, does that mean suasive is archaic, or just used in a particular context?
Suasive is an adjective that, in Linguistics (Grammar), "denotes a class of English verbs, for example, insist, whose meaning includes the notion of persuading and that take a subordinate clause whose verb may either be in the subjunctive or take a modal."
Persuasive is an adjective as well, that means being "good at persuading someone to do or believe something through reasoning or the use of temptation:
an informative and persuasive speech." OR "
She was very persuasive!"
The difference, then, is that while the former denotes a grammatical class for verbs, the second is adopted the way you already know, with people, situations, etc.
EDIT NOTE: In the OED it says that a speech can be "suasive" but considering the OALD and my dictionary didn't have it, I supposed it was an old use or it fell into disuse. So I checked the Ngram on google and it confirmed what Billare said and what I was thinking.