 A variety of objections to Swain’s theory have been proposed in the  literature.[7]  Perhaps the best of these is that presented by Joseph Tolliver (1982, pp. 151–155). Tolliver’s counterexample, which he calls the pendulum case, goes like this: suppose a physics student has learned that from the period of a pendulum (i.e., the time it takes to complete a swing) one can calculate its length and vice versa.  The student measures a particular pendulum and discovers that it has a length L, and calculates that it must have period P. The student also has two general beliefs about pendulums, namely (1) that if x is a pendulum of period P, then x is a pendulum of length L, and (2) that if x is a pendulum of length L, then x is a pendulum of period P. We may suppose that it is clear in this case that the student’s belief about the period is based (at least in part) on her belief about its length, but her belief about its length is not based on her belief about the period. But, Tolliver claims, the student’s belief about the period pseudo-overdetermines her belief about the length of the pendulum, and hence gets counted, on Swain’s theory, as the basis of her belief about the length of the pendulum. This is so because, according to Tolliver, if the actual cause of the student’s belief about the length had not occurred, and if the student still had both her belief about the period and her belief about the length, then her belief about the period would have caused her belief about the length.