If a property can be had at one time and lacked at another, then propositions predicating that property of an individual should vary in truth-value across times.

The motivations for temporalism are both metaphysical and semantic. On the metaphysical side, A-theorists about time (see the entry on time) think that corresponding to predicates like “is a child” are A-series properties which a thing can have at one time, and lack at another time. (Hence, on this view, the property corresponding to “is a child” is not a property like being a child in 2014, since that is a property which a thing has permanently if at all, and hence is a B-series rather than A