Mark Liberman provides the best discussion you are likely to see of the tangled history of these words, and specifically of the use of “personal infer,” the oldest example Mark could find being “Why, in the name of all that’s consistent, you don’t mean to infer that you love this fellow?” from John Brougham’s play Flies in the Web (Mark couldn’t find a date for the play, but it’s clearly before Brougham’s death in 1880). Mark’s conclusion:
So whatever is going on with infer as “imply”, it’s not just a recent mistake in linking similar words to complex concepts. There’s a long history of erratic specialization (from the original sense “bring in” to the much more limited meaning “deduce”) and sporadic generalization (from contexts where “deduce” might be taken to mean “suggest”).
was amused to see had thought that the first comment is was classic prescriptivist panic: “You’re right it is interesting, but I’ll bet you’re not going to start using non-personal infer instead of ‘imply’ yourself, are you? There’s no reason to do so.” Danger! Danger! Unacceptable usage sighted and possibly defended—fire the torpedoes!… but it turns out it was by our old pal Arthur “A.J.P.” Crown, and was not intended as prescriptivist panic at all. Once again my lovely rhetoric is shot out of the sky!