Passive affects from external determination; active affects from adequate causation
Formal Statement
We are passive when external causes determine us through inadequate ideas, producing affects that diminish our power. We are active when we are the adequate cause of what follows from our nature, producing affects that express and enhance our power. Passive affects constitute human bondage (Part IV); active affects, arising from reason and intuitive knowledge, constitute the path toward freedom (Part V). The entire ethical project of the Ethics rests on transforming passive affects into active ones by achieving adequate understanding.
In Plain Language
Here is the trajectory of the whole Ethics in miniature. You started with parallelism: one reality, two descriptions. You found that being is striving. You found that striving becomes feeling — joy when power rises, sadness when it falls. Now you see the fork in the road. If your emotions are driven by confused ideas of external things you do not understand, you are in bondage — tossed around by forces you cannot grasp. But if you come to understand those forces adequately, the same conatus expresses itself as active joy, as the mind's own power of understanding. Freedom, for Spinoza, is not the absence of necessity — it is the transformation of passion into action through knowledge. Parts IV and V will work out the details, but the essential architecture is already here.
Why This Follows
From ce-04, the active/passive distinction tracks adequate versus inadequate ideas. From ce-14, all affects reduce to joy, sadness, and desire. From ce-15, complex emotions are compositions of these primitives shaped by cognitive quality. The recap synthesizes: passive affects arise when we are only partial causes (inadequate ideas, external determination); active affects arise when we are adequate causes (clear understanding). This maps onto the Ethics' larger arc: Part IV analyzes bondage to passive affects, Part V shows how adequate knowledge transforms them.
The path from emotional bondage to freedom runs through the transformation of inadequate ideas into adequate ones — turning passions into actions.
Connected Concepts
Spinoza claims that understanding the cause of a passive emotion already begins to transform it into something active. Have you ever experienced a negative emotion losing its grip on you simply because you came to understand why you were feeling it?
Path complete!
You now see how all emotions trace back to conatus and the increase or decrease of your power. Passive affects trap you; active affects free you. This is Spinoza's psychology.