4.116 Everything that can be thought at all can be thought clearly. Everything that can be said can be said clearly.
This seems to be aimed at Frege, who thought he had to hint at some important points and count on his readers to grasp what he was trying to get at. Schopenhauer might also be a target, perhaps surprisingly. Frege and Schopenhauer attack obscurity and praise clarity and precision, yet Frege's reliance on hints is well known, and Schopenhauer endorses mysticism. On p. 610 of volume II of The World as Will and Representation he writes that "all religions at their highest point end in mysticism and mysteries, that is to say, in darkness and veiled obscurity." On the next page he writes about what mystics find but then adds that "nothing of this is communicable except the assertions that we have to accept on his [i.e. the mystic's] word." In some ways Wittgenstein seems to be agreeing with Schopenhauer here, but he also appears to imply that mystics can have no incommunicable thoughts.
Wittgenstein here also makes a point about meaning. Where there is meaning, there is clear (i.e. precise, determinate) meaning. So can what the mystic finds have any meaning at all?