In The Heart Of Things
But now, how comes knowledge into the middle of the things?
In order to be deemed physically real, a thing must show a certain constancy in its appearances. This is a criterion that, though naturally used, did not become part of physical theory. For it is much too fundamental. It is rather logical. That is where it belongs, in the sphere of mental things, the sphere of knowing.
Actually we have made out this steadiness as being essential for knowledge; it is precisely that what we have used to define knowledge. Which, of course, makes sense only if it is complemented by its counterpart, the change that defines activity.
Not only is knowledge the firm ground we can rely on, resting in sameness like a rock in the rough sea of change and activity; it also manifests itself in characteristic activity. It is a bridged and grasped difference; it is captured activity, calmed down, but always potentially present.
And that is exactly how we have to imagine material things, as full of and driven by activity. But this activity is tamed and manifests itself in continual appearances of the things, in their interactions with other things. Physically these determine the things’ mass and energy, for example. These two terms correspond, in the main, to knowledge and activity, though the latter are meant to be much more general, principal, marking a logical conception.