Since it has generally been accepted that to Spinoza attributes are real features of substance, the interpretation of his attribute definition has become a notorious problem. The reason is that interpreters have failed to see that the definition formulates a purely epistemological account of the state of affairs. The article presents and justifies such an interpretation. It will be shown that the definition in spite of its epistemological character implies a real ontological definition, which specifies the critical features of an (...) attribute. As to the reason why Spinoza has stated the definition in an ‘indirect way’, it is shown that it is likely that he has done so in order to have a more efficient, a more unambiguous and a more elegant definition. The relevance of the new interpretation is not only that it provides us with an interpretable, transparent attribute definition, but it also contributes to the establishment of a coherent picture of Spinoza’s metaphysics around this definition. (shrink)