"Sir," said he, "what entitles Sheridan [this is Thomas, father of Richard Brinsley S. the playwright; he had undertaken to write a pronunciation dictionary] to fix the pronunciation of English? He has, in the first place, the disadvantage of being an Irishman; and if he says he will fix it after the example of the best company, why, they differ among themselves. I remember an instance: when I published the Plan for my Dictionary, Lord Chesterfield told me that the word great should be pronounced so as to rhyme to state; and Sir William Yonge sent me word that it should be pronounced so as to rhyme to seat, and that none but an Irishman would pronounce it grait. Now here were two men of the highest rank, the one the best speaker in the House of Lords, the other the best speaker in the House of Commons, differing entirely."Incidentally this is related to the fact that the predecessors of words ending -ee- and -ea- in Modern English were pronounced differently -- resp. as "closed" and "open" forms of "ay" -- but spelled alike in Middle English; it was during the transitional period, when -ee- was pronounced in the modern way but -ea- was pronounced to rhyme with -ay- (e.g. where you, great Anna, whom three realms obey / do sometimes counsel take, and sometimes tea), that English spelling was settled; if the commenter is right the distinction was codified in spelling (by Johnson and others) just as it was becoming obsolete.
And here's Nunberg on a similar issue, which I think comes off as endearingly unprissy of the Augustans though of course it's nothing of the sort:
Or to take an example I'm more familiar with, consider the 18th c. blurring of the nuclei of words like line and loin, which turns up several times in the Essay of Criticism:
In Praise so just, let ev'ry Voice be join'd,
And fill the Gen'ral Chorus of Mankind!
And praise the Easie Vigor of a Line,
Where Denham's Strength, and Waller's Sweetness join.
Good-Nature and Good-Sense must ever join;
To err is Humane; to Forgive, Divine.
One notable point here is that this confusion was phonetically conditioned, limited to vowels before /n/, /l/ and some other sonorants, particularly when preceded by /p/ and /b/ (as in point and boil). Nobody rhymed toy and sigh as far as I know. So the rhymes here turned on a perception of phonetic closeness or identity, not simply a rhyming convention. A second is that the confusion left several doublets in its wake (rile and roil, for example) as well as some dialect variation: Dickens had his lower-class characters saying spile for spoil and jint for joint. A third is that the confusion was noted, and sometimes criticized as "abusive," by contemporary writers.