 Heytesbury, like Kilvington, classifies all capacities as mutable or immutable. A mutable capacity is capable of more and less, and both affirmative and negative parts of the division might be assigned. For example, with respect to Socrates, a mutable power of lifting (an active capacity) a minimum quod non is assigned. For a passive capacity the maximum quod non is assigned, e.g., a maximum visible body which cannot be seen at a given distance. An immutable capacity acts in a determinate way, so it produces only the one effect it actually produces. Therefore, the affirmative part of the division is always assigned as a boundary for immutable capacity. Thus, e.g., there is a maximum distance which, ceteris paribus, Socrates can traverse in an hour by a speed which increases uniformly from A to B degree ([RSS] 1494: fol. 29vb; Wilson 1960: 73).