PROPOSITION XXVI. The human mind perceives no external body as actually existing unless through the ideas of the modifications of its body.

Demonstration. If the human body is in no way affected by any external body, then…the idea of the human body, that is to say…, the human mind, is not affected in any way by the idea of the existence of that body, nor does it in any way perceive the existence of that external body. But in so far as the human body is affected in any way by any external body, so far… does it perceive the external body
–Q.E.D.
Corollary. In so far as the human mind imagines an external body, so far it has not an adequate knowledge of it.
Demonstration. When the human mind through the ideas of the modifications of its body contemplates external bodies, we say that it then imagines…, nor can the mind…in any other way imagine external bodies as actually existing. Therefore…in so far as the mind imagines external bodies it does not possess an adequate knowledge of them — Q.E.D.
–Spinoza, ‘Ethics’

If one carefully attends to Spinoza’s understanding of substance as conatus, one can probably see how Spinozist substance can be read as a rupture from both the Cartesian, and Kantian, conceptions of subject-object duality. A rupture that is, if one may be allowed to speak in Alain Badiou’s terminology, subjective materiality in its singularisation. So, what is often termed Spinoza’s objectivism, is, in my opinion, ontological subtraction from the the subject-object duality, and its constitutive horizon of a symmetrical and thus idealist dialectic.

Therefore, the Spinozist substance, as far as I am concerned, is unrelenting antagonism to such a horizon of dialectical symmetry. And precisely for that reason is his substance or being — or his substantive being — nothing but the antagonism to the dialectic, which thinks dialectically precisely to preempt its subsumption by the dialectic, and its own interruption as antagonism thereof. All this, in order to keep being the antagonism or ontological excess it is.

In such circumstances, there is no question of Spinoza being a solipsist. For, singularity, particularly if it’s thought in terms of the relentlessness of antagonism to the dialectical machine, can by no means amount to solipsism. Spinoza, then, is, for me, certainly not a solipsist. But I wouldn’t call him an objectivist either. Pace Macherey, I read him as a materialist who philosophically prefigures the materialist dialectic.

One will see Spinoza as a solipsist only when one conceives materialism as objectivism, and does not grasp materiality as ontological excess — the actuality of uninterrupted exceeding of the subject-object duality and the horizon of symmetrical dialectic this duality is constitutive of. And it’s this ontological excess that is the approach at work in Marx’s theoretical practice of critique of political economy as is its philosophical presupposition.

This Marxian critique in its operation as “practical practice” — which would render such “practical practice” praxis — would be nothing but precisely this actuality of uninterrupted exceeding of the subject-object duality and the horizon of symmetrical dialectic it is constitutive of. In other words, Spinoza’s substance is subjectivity as a process of desubjectivation. Or, conversely,. Spinoza’s being is a subject that is substance precisely in being-aftersubject.