Full Idea
The mind and the body are one and the same individual which is conceived now under the attribute of thought, now under the attribute of extension.
Gist of Idea
Mind and body are one thing, seen sometimes as thought and sometimes as extension
Source
Baruch de Spinoza (The Ethics [1675])
Book Reference
Cottingham,John: 'The Rationalists' [OUP 1988], p.132
A Reaction
I suppose we might now call this 'property dualism'. It is odd that when you examine one property, the other is nowhere to be seen.