 Condition (3) is intended to handle the pendulum case discussed above. In the pendulum case, the student measures the length of a pendulum and thereby comes to believe that it has length L. On the basis of this measurement and other truths she knows about pendulums, the student is able to calculate the period of the pendulum. Thus, the student’s belief about the length serves as a reason for her belief about the period. The apparent problem for Swain’s view was that the students belief about the period also seemed to be counted as a reason on which her belief about the length was based, when in fact the basing relation went in the reverse direction. Tolliver’s theory attempts to handle this problem by means of condition (3), which is intended to specify the direction of the evidential support relation. Once the student measures the length and makes the inference about the period, the student’s estimate of the likelihood that the pendulum has period P would increase. However, the student’s belief about the period of the pendulum would not, according to Tolliver, increase the estimate of the likelihood that the pendulum has length L because the student’s belief about the length is needed to calculate the period.