Summary
Part I: Concerning God
Spinoza defines substance as what exists and is conceived through itself. Two substances sharing an attribute cannot be distinct, and an absolutely infinite substance must exist. God possesses infinite attributes and nothing can exist or be conceived without God.
Finite things are modes following from divine nature. God acts from the necessity of that nature rather than from arbitrary choice. The Appendix criticises final causes and the tendency to treat human usefulness as the purpose of nature.
Part II: The Mind
Thought and extension are divine attributes. The order and connection of ideas is the same as the order and connection of things. The human mind is the idea of the human body, making mental and bodily events parallel expressions of one reality.
Imagination arises through bodily encounters and often supplies fragmentary knowledge. Common notions and reason produce more adequate understanding. The will is not a separate faculty free from causal determination; particular acts of affirmation belong to particular ideas.
Part III: The Emotions
Spinoza analyses people as parts of nature. Each thing strives to persevere, and human desire expresses this striving. Joy is a passage to greater perfection or power; sadness is a passage to lesser power.
Love, hatred, hope, fear, pity, envy and other affects arise through ideas of causes, associations and imitation. Passive emotions occur when people are only partial causes of what happens within them.
Part IV: Human Bondage
Bondage is the inability to moderate emotions. Knowledge alone may be defeated by a stronger affect. Good and evil identify what assists or obstructs movement towards a more powerful human nature.
Reason recommends self-preservation, adequate knowledge, friendship and cooperation. Nothing is more useful to a person than another person guided by reason. Political and social arrangements can help people live more securely and rationally.
Part V: Human Freedom
Understanding an emotion as part of a causal order makes it less passive. Forming clear ideas, connecting affects with many causes and viewing events under eternity increase the mind’s activity.
The intellectual love of God is joy accompanying adequate knowledge of necessary reality. Blessedness is not payment for suppressing desire; it is the active power through which destructive passions lose their dominance.