ista- (2) vb. "know", pa.t. sintë(IS, LT2:339, VT48:25). This past tense Tolkien called "certainly irregular" (VT48:25, where an alternative pa.t. isintë is also mentioned, but sintë is said to be the older form; compare editorial notes in VT48:32. Ista- is also used for "can" in the sense of "know how to", as in istan quetë "I can speak (because I have learned (a) language)" (VT41:6) Passive participle sinwa "known, certain, ascertained" (VT49:68)
ista- (2) vb. "know", pa.t. sintë (IS, LT2:339, VT48:25). This past tense Tolkien called "certainly irregular" (VT48:25, where an alternative pa.t. isintë is also mentioned, but sintë is said to be the older form; compare editorial notes in VT48:32. Ista- is also used for "can" in the sense of "know how to", as in istan quetë "I can speak (because I have learned (a) language)" (VT41:6) Passive participle sinwa "known, certain, ascertained" (VT49:68)