 If such circularity were avoidable, then it would be good for us to avoid it. Unfortunately for us, the constructive empiricist might say, it is not avoidable (Monton and van Fraassen 2003, 415–416, maintains this line). Advocates of constructive empiricism might insist that any search for a Cartesian-style guarantee of the correctness of our theory of observability is a search in vain. We have to accept some such theory, imperfect though it may be, and modify our acceptance if experience proves that acceptance to be misplaced.