P1: Our Mind does certain things {acts} and undergoes other things, viz. insofar as it has adequate ideas, it necessarily does certain things, and insofar as it has inadequate ideas, it necessarily undergoes other things.

Dem.: In each human Mind some ideas are adequate, but others are mutilated and confused (by IIP40 S). But ideas that are adequate in someone’s Mind are adequate in God/Nature insofar as he constitutes the essence of that Mind {only}6 (by IIP11 C). And those that are inadequate in the Mind are also adequate in God/Nature (by the same Cor.), not insofar as he contains only the essence of that Mind, but insofar as he also contains in himself, at the same time, the Minds of other things.

Next, from any given idea some effect must necessarily follow (IP36), of which effect God/Nature is the adequate cause (see D1), not insofar as he is infinite, but insofar as he is considered to be affected by that given idea (see IIP9). But if God/Nature, insofar as he is affected by an idea that is adequate in someone’s Mind, is the cause of an effect, that same Mind is the effect’s adequate cause (by IIP11 C). Therefore, our Mind (by D2), insofar as it has adequate ideas, necessarily does certain things {acts}. This was the first thing to be proven.

Next, if something necessarily follows from an idea that is adequate in God/Nature, not insofar as he has in himself the Mind of one man only, but insofar as he has in himself the Minds of other things together with the Mind of that man, that man’s Mind (by the same IIP11 C) is not its adequate cause, but its partial cause. Hence (by D2), insofar as the Mind has inadequate ideas, it necessarily undergoes certain things. This was the second point. Therefore, our Mind, etc., q.e.d.

Cor.: From this it follows that the Mind is more liable to passions the more it has inadequate ideas, and conversely, is more active the more it has adequate ideas.