William of Ockham (c. 1288–1347)

William of Ockham was an English Franciscan friar and philosopher who argued that only individuals [Page 1435]exist, not essences or forms, which have no existence apart from the human mind. Ockham's theory of time is an application of his general principle that entities should not be multiplied unnecessarily. Thus, the soundest argument is one that rests on the fewest assumptions, factors, variables, or causes; this principle is still commonly referred to as “Ockham's razor.” According to this principle, Ockham acknowledges only a nominal definition (definitio quid nomi-nis) of time, not a real one. That is, the word time does not signify a particular thing, but just the continuous movement of the heavens. Insofar as that movement can be measured, time also signifies (con-significat) the human mind and its activity of ordering things as occurring earlier or later.

Ockham stresses that in order to recognize time, it does not suffice just to be aware of some change; rather, change has to be understood as motion (motus), as a continuous process in which the particular instances of change happen. Thus, directly (in recto), “time” signifies a processual, continuous motion, and indirectly (in obliquo) the awareness of that motion in the human mind. By identifying in this way time and motion, which are distinguished only by activity of the mind, Ockham leads the medieval predilection for defining time via movement as an equivalent of time to its ultimate consequence: While most thinkers before him identified the “matter” of time with motion but granted to it a form of its own as did Albert the Great, Ockham denied that time even had a separate existence in this restricted sense. Consequently, he also denies that the sentence “time is a thing being (tempus est ens)” is true in the sense of “time exists”; rather, it is true only by virtue of the truth of other sentences concerning the existence of past time, of present time, and of future time. In reality, however, only the actual moment (instans) exists. All prior moments no longer exist, and all future moments do not yet exist; they are “a pure nothing” (purum nihil). Because of this, an activity of the mind is necessary to bring about that successive motion that we call time: Our mind is able to recognize things that it itself imports (importât) into the world, such that they exist in a certain way outside of the mind (extra animam), but due only to the mind's activity. This holds true for past and future moments of time, which do not exist in themselves but whose potential existence as moments that have been and moments that will be can be actualized by our cognition, such that we grasp the continuous succession of such moments, which we call time, though all but one of its elements actually do not exist and especially not apart from things in the process of change. This interpretation of Aristotle's statements in the fourth book of his Physics relies heavily on Averroes's interpretation of the same texts, which are quoted frequently in William of Ockham's treatise on time.

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