The distinction between the words blessèd (/ˈblɛsəd/) and blessed (/blɛst/) (see Grammarbook) appears to be wearing thin in modern language, possibly due to reduced accent usage and its resultant lack of different pronunciation between the two terms.
Wiktionary refers to the word as
poetic, dated
And most damningly of all as an
Alternative form of blessed (verb)
While I understand that little usage of terms such as blessèd and cursèd cause them to get blurred with their verb counterparts, some adjectives like naked, talented, sacred are still used, always written without the accent. In some legal and political circles†, learnèd is still used for specific traditional purposes but it is now starting to fade.
What is the history behind the distinction in pronunciation?
The reason why some of these words are pronounced with /əd/ is explained by the answers to this question: "Why pronunciation of “Crooked” is “Crook-ked”?"
David G said:
If the normal form of the word (crook, twist) ends in t or d,
the -ed is enunciated (such as wanted or bedded).
This explains the pronunciation of talented, but not that of naked, sacred, or blessed. The pronunciation of naked is however explained by coleopterist's answer to this question: Where does “wicked” get its /ɪd/ from?
According to A Critical Pronouncing Dictionary and Expositor of the
English Language, 1839,The adjectives naked, wicked, picked (pointed), booked, crooked, forked, tusked, tressed, and wretched, are not derived from verbs,
and are therefore pronounced in two syllables. The same may be
observed of scabbed, crabbed, chubbed, stubbed, shagged, snagged,
ragged, scrubbed, dogged, rugged, scragged, hawked, jagged; to which
we may add, the solemn pronunciation of stiff-necked; and these when
formed into nouns with the addition of ness, preserved the ed in a
distinct syllable, as wickedness, scabbedness, raggedness, &c.
However, the answers to "Pronunciation of "Blessed"" don't describe the historical origin of the different pronunciations of this word as adjective and verb form.
What is the history behind writing these words with accents?
How common was it in the past to write these words with grave accents, and in what contexts did people do this? There has already been a question about the use of this accent in Shakespeare's work: "Are there any pairs of words like “beloved”/“belovèd”, “learned”/“learnèd” that maintain a semantic difference to the present day?" But it's not clear from that if Shakespeare's original manuscripts use it, or if it something that's been added to modern editions to help readers find out the meter.
Why have these words generally lost their accents?
Has this then lead on to them losing their differing pronunciations?
Finally, should one use a grave accent (è) here or should one just let context dictate pronunciation?
†Interestingly, Hansard don't include accents at all, even when one looks back into the 18th and 19th century records. This may, however, be a result of typewriting and modernising of the records.
Best Answer
Looking at the original spelling in Shakespeare's sonnets, he was somewhat inconsistent. But he never used an accent, and he generally used belov'd for the two-syllable pronunciation (which the OP spells beloved) and beloved for the three-syllable pronunciation (which the OP spells belovèd).
It's not clear to me that there was ever any time when the accents were usually included in normal prose (as opposed to poetry, where accents were used to make sure it was pronounced as intended). I've checked samples of the phrase learned man from the 17th to the 19th centuries in Google books, and I haven't found any accent marks in prose.
For Shakespeare, there is a website that gives the original spelling for all the sonnets (click on the link and scroll down until you find it).
See Sonnet CL:
(note that he leaves out the apostrophe in rais'd.)
Also see Sonnet CXXVIII, which uses both blessed and blest in the original spelling.
And also Sonnet II, which uses gaz'd, totter'd, askt and deserv'd in the original spelling.