What causes the difference in vowelization of the Hebrew word for "what"? In some contexts it is מֶה, in others - מָה, and in yet others - מַה. The hypothesis that an acquaintance and I converged on was that only when preceding a guttural (or lower) consonant is it מֶה, but this was falsified by "במה מדליקין".
What is the rule governing this change?
(Apologies for the imprecise transliteration in the title. My American English-speaking conscience couldn't bear to make a kamatz an 'o' and I saw no better alternative.)