From what I understand, すら is commonly used with the negative conjugation (~ない, ~なかった) of verbs.
For example:
「ひらがなすら書けない。」 I expected (him) to be able to write hiragana. But even hiragana, (he) can't write.
「涙すら出なかった。」 I expected tears to fall. But even tears, didn't fall. (I expect him to cry but he didn't even wept a tear.)
Basically I was wondering is it grammatical to use すら with the positive conjugation of a verb?
For example, can 「涙すら出た。」 be considered grammatical, assuming the context is that the speaker expected "no tears to fall", but indeed "tears did fall"?
すら
does not mean "unexpectedness", but rather means "the least likely" (a comparative notion). If the event mentioned happens, then the unexpectedness does not fall on the thing mentioned, but falls on the more likely things on the scale. Correct translations will be 1. "He can't even write hiragana (which is the least likely thing he can't do, so I expect he can't write anything else.)" 2. "Even tears didn't fall (which is the least likely thing to not happen, which means indicates that it was indeed a sad situation.)" – user458 May 27 '12 at 16:17