I have heard that when saying certain words the m'lera m'leil is meakev
"For example, v'ahavTA ("and you shall love) is correct, but that v'aHAVta would mean "and you loved" would be incorrect. or v'aSAFta v'asafTA. vachalTA - VaCHALta. and several other instances where the emphasis would change the tense
Is this correct? is there a source? i did not see this addressed in a quick look, where pronunciation of the letters is discussed, but may have been looking in the wrong place.
moshe rubin, brooklyn, new york
As you have noted, v'aHAVta means "and you loved" in the past tense rather than a command, whereas the correct v'ahavTA means "and you shall love", a command. One should be careful to pronounce it correctly since the incorrect pronunciation changes the meaning (Teshuvos v'Hanhagos of Rav Moshe Shternbuch Vol. 2, Orach Chaim #45 pg. 41).
I'm not sure why v'aHAVta is not converted to the future tense by the Vav according to Rav Shternbuch. I am also at odds to explain why v'Asafta or v'Achalta in the Kerias Shema, which appear to be part of a promise of Berachah in the future tense, should be in command form.
Kol Tuv,
Avraham Phillips
Regarding the accent on a word changed from past to future with Vov HaHippuch, the general rule is that the accent moves later (mil'ra instead of mil'eil).
This does not happen if the third root letter is a Heh, unless there is reason due to the word afterwards.
See an extract from excellent weekly email publication Toras Hakoreh (tameytora@gmail.com) in Parshas Emor, including a quote from the Redak.
Kol Tuv
Meir Eliezer Bergman
... this also may not happen if the following word is accented on its first syllable (nosog achor) when the accent is moved back mil'eil (e.g. v'oCHALto Shom)
See also extract from excellent sefer Mafteach Hadeles.