Mind does not move body; body does not move mind
Formal Statement
Body cannot determine mind to think, nor can mind determine body to motion or rest. All modes of thinking are caused by other modes of thinking; all modes of extension by other modes of extension. The causal chains within each attribute are self-contained.
In Plain Language
Descartes imagined the soul nudging the body through the pineal gland. Spinoza says that picture is incoherent: a thought cannot jump the attribute barrier and shove matter around, and vice versa. If you raise your arm, the physical cause is prior physical states of your body, not a disembodied "decision." The decision and the neural cascade are the same event in two descriptions. This means we cannot explain emotion by saying the body "causes" feelings in the mind. We need a different framework.
Why This Follows
From ce-01, each attribute is conceived through itself alone (I, Definition 4; II, Proposition 6). Thought-modes are caused by thought-modes, extension-modes by extension-modes. Cross-attribute causation is ruled out structurally, not just empirically.
There is no causal arrow from body to mind or mind to body; emotional life must be understood within parallelism.
If mind never causes bodily action, what exactly is happening when you "decide" to stand up and then stand up?