Why does Spinoza believe that God must exist?

For Spinoza, what is a substance? How many are there? What is one of them?

For Spinoza, what kinds of things are humans in relation to God?

For Spinoza, in what sense do humans have two aspects? In what sense are they one thing?

For Spinoza, in what sense are humans free? In what sense is God free?

What are the three primary emotions for Spinoza? In what way are they primary?

For Spinoza, what kind of being can have pleasure and why? What is it about Spinoza's conception of pleasure makes it such that God cannot share in it? What is Spinoza's conception of pleasure?

On Spinoza's view, why should the rational man join society and obey the law?