 As perception is in this context replaceable with knowledge, the principle is equivalent to its modern counterpart, save the emphasis on active consideration of the problem (i.e., attention), which appears to correct the principle for the limitations of human agents. The principles for both first and second-order knowledge are based on the same evidence ([RSS] 1494: fol. 13vb [1988b: 447–448]). Heytesbury also holds the contraposition of (4) ([RSS] 1494: fol. 13vb [1988b: 448]).