That which cannot be conceived through another thing must be conceived through itself.
Spinoza, Ethics, the second axiom
Such an axiom or rather an advice seems to be easily understood if we remind the way of successive exclusions followed by Descartes in his Meditations. But since Descartes made his way easier by including the kinds of knowledge in some large category, as, for instance, sensibility, his repeated exclusions commits to the acceptance of these categories, even if in the mode of exclusion. The kinds of knowledge excluded are in fact stated as really existent and just wait for Descartes’ discovery of certainty for imposing themselves in a compulsory manner to the results of knowledge.
From Descartes’ experience, but also from the current experience of thought, we may infer as a common fact about philosophical accounts that what they leave apart as general categories with the goal of knowing some specific objects of researching always returns and impedes the discovery of things in their peculiarity. Differently from the spread of Spinoza’s Ethics, we commonly fail to acquire the knowledge of an object while we cease to be concerned of another individual thing, as, for example, our bodily existence, by classifying it in a large category, as the concept of ‘body’ in our case. We may prove this pointing out to the common tendency to represent soul as almost a pair of the body. Yet, some particular manners of bodily action omitted when it was advanced the concept of a ‘body’ say more about the affective life than we imagine by separating it from the body. Paradoxically, if we do not commit to this concept and assume the particular manners of bodily existence, we owe less to the body for our conceptions. Thus, one who reads in the circulation of blood something about our ever moving thoughts and their enslavement to the functioning of our lives comes to know something about the life itself, not about body.
Therefore, Spinoza’s advice for an excurse in the field of excluding the things that can be conceived through another thing should be taken as an investigation of things placed on the same level of generality. Only this way shows the knowledge as the effort of grasping the reality. For only when we have all the things surrounding us, not partially detached in general classes, there is possible to seize by thought the simple and common fact of being altogether with the whole of the things and human beings, and with their thoughts and words, too.
Spinoza’s interest is also to discover the reality conceived by him as the substance which has self-existence. That which is conceived by another thing have to be excluded, but, contrary to Spinoza, such effort has to be done as regards the act of conceiving things. The act of conceiving things is the main source of placing them aside from observing their existence, as Descartes did during his meditations.
In the act of describing the reality, we met the tendency of conceiving things as Spinoza’s substances. Who would refuse to such a minor thing as a pair of shoes to be a self-existent thing? And who would refuse this to a human being? All of these are figured out as independent realities in the virtue of being named with singular names or proper names. Also, because of their spatial existence. But the space is not conceived as the limit of the thing, as Aristotle’s stated in Physics, being in fact understood as a ‘here’ or ‘there’, as a collection of points that subdue an existent thing while testify its existence.
The language and the space conceived as an aggregate of points give both birth to the conception of the things as substances, though both of them ignore in fact their existence. Without being considered in their existence and, accordingly, in their power to resist to a simplifying view of them as mere names or spatial points, things and men are easily melted together, so that they come to be seen as depending one on another for their existence.
Therefore, Spinoza’s axiom cannot be accepted as a simple demand of excluding some things in order to know the remaining substances. First of all it is necessary to disentangle them from the chains where they are included through language and spatial representation. Afterwards, their self-existence as substances would not seem as a matter of a simple separation of each by others, but as independent sources of attracting the remaining things to themselves. A man who assumes his existence is not a separated and singular being, but one who attracts to him the rest of existing things. For the language and spatial representation are manner of ignoring the existence, the thought should be considered as the way of assuming your own existence, and for assessing the existence of other things. Surely, not that thought that searches for its conceptual separation, as it is the case of Cartesian philosophy.