When we conceive a being which has the reason of its changes within itself, we conceive an active being.
When we conceive a being which has within itself the reason of the changes of other beings, we conceive an active being.
When we conceive a being which knows, wills, perceives, or has consciousness in any way, we conceive an active being.
Hence activity may represent three things to us: the origin of its own changes; the origin of the changes of others; and consciousness.
133. The first kind of activity can belong only to changeable beings; the second also to immutable beings, which are causes; the third is an activity which belongs to mutable or immutable beings, abstracting absolutely the idea of causality.
134. The general relation of principle of its own or another's changes, is an indeterminate idea; consequently the only activity of which we can have an intuitive idea is that of intelligence, of will, and in general of whatever relates to the phenomena which require the perception called consciousness.
135. We must consider consciousness as an activity, and include in this order the idea of intelligence and will abstracted from all relation to their own or another's changes, unless we mean to say that God was from all eternity an inactive being, because he had no other action than the immanent acts of knowing and willing.
136. Therefore not all activity is transient, but there is a true immanent activity, of which we have an intuitive knowledge in the phenomena of our consciousness.
137. The activity which we can conceive in bodies is reduced to a principle of their own changes or those of some other being; it is therefore something of which we can have no intuitive knowledge. In fact, we are in relation with bodies only by means of the senses, which present but two orders of facts with respect to corporeal nature; subjective facts, or the impressions which we experience and call sensations, and which we believe to emanate from the action of bodies upon our organs; and objective facts, that is, extension motion, and the different modifications which the senses discover in extended things which move. Neither the first class of facts nor the second give us an intuitive idea of the activity of corporeal beings.
Subjective facts or sensations are immanent, that is, are in us, not in the things; and inasmuch as subjective tell us nothing of what is outside of us, but only what is within us. Even supposing sensations to be a true effect of the activity of bodies, this activity is not presented in the effect. When our hand is warmed by the fire we have the intuitive perception of the sensation of heat, inasmuch as it is in us; if we suppose that this sensation is really an effect of the activity of the fire, we know the relation of our sensation to this activity considered in general, and indeterminately as the origin of our sensation; but we do not know the activity intuitively in itself, because as such it is not represented in our sensation.