Editor’s note: This is the fourth in a series of essays on Dutch philosopher Benedict Spinoza.
The ancient Greeks and Romans recognized three divisions of human enquiry: logic, physics and ethics. When constructing his philosophical system, Spinoza followed this traditional scheme, and I shall do the same in explaining it.
Spinoza, following the ancients, had a broader notion of logic than what is current in academic circles. Now it refers to a highly sophisticated and technical discipline of constructing sound arguments and judging them. Spinoza imagined something more fundamental than this: a method that would set the mind on a secure course leading to the discovery of truth. This was also a central theme of the scientific revolution, for, it was asked, how can new knowledge be found, unless the mind is capable or fit to find it?
Among Spinoza’s literary remains, there is a work, perhaps his earliest work, which is devoted to this task. He entitled it Tractatus de Intellectus Emendatione, or Treatise on Reforming the Intellect, or How to Improve your Mind in the search for Truth. It is unfinished, youthfully ambitious, and very interesting.
Spinoza imagined himself at a crossroads in life having to choose which road to follow. He considered the usual options: wealth, honor, pleasure, to which he added another — truth.
He rejected the first three. Neither one of them, nor even all of them together, could bring lasting happiness. Only the last could ensure it, for, he imagined that the search for truth culminates in the truth of all truths, which is of eternal and infinite value, “an eternal and infinite thing that feeds the mind with a joy entirely exempt from sadness.”
He did not entirely give up on the other three, for everyday existence depends on them. He would seek modest wealth, enough on which to live, and he would welcome innocent pleasures, especially friendship. As for honor, he would try to live a respectable life. And, in fact, this is just the sort of life that Spinoza lived.
But how do we discover this ultimate truth? Spinoza’s answer is by having true ideas — remember he is a rationalist, and recall the straight line: We can be certain that a line is straight if and only if it is the shortest distance between two points. And our certainty that this is so depends merely on our having a true idea of a straight line. But this is not the truth of all truths. I am reminded of a remark of Hegel, when he embarked on a similar project: “the truth is a whole in the form of a system.”
This applies to Spinoza perfectly.
He imagined that acquiring ideas is like exercising the body. The mind becomes more fit the more it acquires ideas and systematically arranges them, first of abstract things like lines and planes and solids, and further by acquiring ideas of natural things, and artificial things, for nothing we humans invent or manufacture is altogether outside of nature. And all of this leads to the all-encompassing idea of Nature itself, which represents also power of existence, and is, accordingly, the Idea of ideas, and the Truth of all truths, like Aristotle’s universe.
But what makes any idea true? Spinoza falls back on Aristotle. Remember, Aristotle supposed that the world consists of particular things. A true idea of a thing is just the idea of “what it is to be that thing,” which enables us to distinguish one thing from another, not to confuse them. This true idea of a thing is the product of experience, of observing and comparing, whereby we gradually approximate the complete idea of the thing. We call this idea the essence of the thing; it consists of the attributes or properties of anything by which it is itself and not another. This conformity of an idea with its object makes it true.
But how do we reach this goal? Let’s begin at the beginning. Spinoza writes that the first and most immediate object of the mind is a body, not just any body, or anybody’s body, but one’s very own body, a claim that is easy to verify. If we think of knowing not as a reflective state but as an activity, a kind of mastery, and as organic, we can find evidences of it in the behavior of all animals.
Watch any squirrel leap from branch to branch, or rabbits frolicking in a field, or athletes performing amazing feats with their bodies: running, jumping, avoiding a blocker, batting a ball, pitching, or running to make a catch, and in every instance knowing what their bodies can do and guiding them expertly.
All of these animals know their own bodies completely, not in a cerebral way, but as instruments; their corporeal knowledge is evident in all of their movements. You can confirm this in yourself. If you are sitting, stand up; if standing, start walking or running; descend a flight of stairs, balance yourself on one leg, or go jump in a lake. It’s true, that in dreams, we often seem to lack corporeal sensitivity, we move about without feeling, like ghosts, which is why we call it dreaming.
Scientific knowledge is the end product of a process that begins by drawing this intuitive knowing into consciousness, through observation and comparison of events, and experimentation, interspersed by a sequence of hypotheses, classification of results, generalization and quantification, none of which would be possible if we lacked the first kind of organic knowledge, if we were not born with corporeal knowledge, if we did not know from the very beginning of our lives.
But this knowledge of ourselves, which is an immediate feeling that matures into an idea, is just the beginning of knowledge; we move on to other things, particular and general, concrete and abstract, for observation teaches us that things do not stand alone; things depend on each other, and so we press on until, forming new and more comprehensive ideas of things we reach “that idea which represents the source and origin of the whole of Nature,” which is Nature itself and in which all else inheres. 
Incidentally, Spinoza also suggests that the stronger our minds become in knowing things, the more our capacity for self-control and self-direction increases also, and the more self-dependent we become, the happier we are.
So, what is the truth that the idea of nature encompasses? I will conclude this essay with a very brief summary of an answer.
Nature is the only substance, the only independently existing thing; it is the “cause of itself,” a thing “whose nature cannot be conceived except as existing;” the only particular that does not depend on any other particular, because all other particular things that we encounter depend upon it, proceed from it, inhere in it, and are conceived through it. Everything is a part of nature.
Finally, Nature is God, “a being absolutely infinite, that is, a substance consisting of an infinity of attributes, of which each one expresses an eternal and infinite essence.” Stay tuned.