Attribute
An attribute is what the intellect perceives as constituting the essence of substance. Spinoza identifies two we can know: Thought and Extension.
In depth
Attributes are the fundamental ways substance expresses itself. God has infinite attributes, but human beings can only access two: Thought (the mental) and Extension (the physical). These are not two separate substances but two ways of understanding the same single reality. A thought and the corresponding brain state are the same event described under different attributes.
Why it matters
Attributes are the bridge between Spinoza's monism and the apparent duality of mind and body. They explain how one substance can appear as both mental and physical without requiring interaction between two separate realms.
Source references
- Ethics I.P10 (Definition 4)