Another important fact about Spinoza’s intellectual character is that he was a rationalist. I begin, then, by explaining what this means and how being a rationalist differs from being an empiricist. For it is commonly supposed that empiricism and rationalism are the two poles of modern philosophy. What’s the difference?
To begin with, empiricists believe that all of our knowledge originates in experience; rationalists deny this. John Locke (1632–1704) commonly regarded as the founder of modern empiricism, characterized it well. Here is what he wrote in his “Essay Concerning Human Understanding:”
“Let us then suppose the Mind to be, as we say, white Paper, void of all Characters, without any Ideas; How comes it to be furnished? Whence comes it by that vast store, which the busy and boundless Fancy of Man has painted on it, with an almost endless variety? Whence has it all the materials of Reason and Knowledge? To this I answer, in one word, From Experience: In that, all our Knowledge is founded; and from that it ultimately derives it self.”
One hundred years later, Immanuel Kant (1724–1804) wrote the following, no doubt with Locke in mind:
“There can be no doubt that all our knowledge begins with experience. … But although all our knowledge begins with experience, it does not follow that it all arises from experience.”
Rationalists suppose that the mind already knows something even before it begins to know, that at the very start of thinking about some subject in an endeavor to understand or know it, the mind discovers some first truth that is beyond rational doubt. This is to put it crudely, but it’s a start.
Consider some examples of rational knowledge. I’ll start with Euclid, who wrote the definitive work of classical geometry, which he titled “Elements,” and which is surely one of great monuments of human learning. I recall reading in Carl Sandburg’s biography of Abraham Lincoln how he educated himself by working through the whole work. Spinoza was well versed in it also.
In certain respects, “Elements” is an empirical work. Its theme “geometry” literally means measuring the earth, and the familiar figures he discusses — points, lines, planes, triangles, rectangles, circles and spheres — are all abstractions, rationally refined and idealized, of things observed. The instruments employed in considering them were everyday things: compass and ruler. Just imagine yourself drawing a line or a circle.
However, notwithstanding the everyday familiarity with his subject, Euclid’s purpose was to establish mathematical knowledge on basic principles whose truth was self-evident. A self-evident truth is something that the mind knows to be true simply by thinking it. Euclid called such principles axioms or common notions, supposing that no one with a working mind could doubt them.
“Axiom” is a Greek word, meaning what is regarded as having the most value, or whatever is most worthy to be called true and count as knowledge because it is beyond reasonable doubt. Here are some examples: “Things equal to the same thing are equal to each other.” “If equals be added to equals, the wholes are equal.” “The whole is greater than the part.” Can anyone reasonably doubt them?
Euclid’s contemporary, Archimedes — they both lived and flourished during the 3rd century BCE — described another axiom, by defining a line as extending between two points, and then went on to say that a straight line is the shortest distance between these two points. I will spend the rest of this essay considering this principle, because it is a clear way to understand the peculiar character of Spinoza’s rationalism.
Recall that Plato was a rationalist. He maintained that ideas and principles were best known when the mind transcended its worldly physical trappings. Spinoza disagreed. He regarded the mind and its content as always embodied.
In his major philosophical work, Ethics, Spinoza wrote that the immediate object of an individual mind is its body. Archimedes’ definition of a straight line involves the notion of distance. Now, ordinarily, we calculate distance by sight, for example, looking straight ahead, when out walking, to the next intersection. But it is, I think, even more organic. Unless obliged or forced to remain on a path that may proceed in a roundabout way to our goal, our bodily instinct is to head straight to our destination, that is, we bodily proceed across the shortest distance. Evidence of this is easily discovered, for example, pathways worn in the grass that make a short circuit of the way from one place to another.
In sum, the idea of shortest distance as a straight line seems a matter of animal instinct. But for those, like Spinoza, who believed that the mind is material, there is no real difference between instinct and thought. Instincts are bodily imperatives that translate into thought and practices. They are the rudiments of thought, indeed of all experience. In this respect, we are all rationalists by nature.
So, what is a rationalist? A rationalist is anyone who recognizes that there are indubitable principles with which all thinking begins and on which it is founded, and if they are not self-evident, they can be rationally demonstrated. Rationalist philosophers are those who endeavor to discover these principles, to defend and explain them. Their credibility resides in the fact that every thinking being, that is, every being whose existence and welfare depends in certain respects on thinking, is by nature a rationalist.
The question is, what are those principles. We have considered a few of them. But Spinoza was after bigger game than these. He had read Lucretius and was deeply involved in the new scientific learning. His purpose, as a philosopher, was to discover the very idea or principle of nature, and to demonstrate, using the methods of Euclid, that nature exists and that morality and human happiness depend on a proper understanding of it.
One final note about lines: I recall reading a remark by Gainsborough, or maybe it was Sir Joshua Reynolds, who expressed an artist’s preference for curved or serpentine lines over straight lines. Curved paths have a charm that the straight path does not, although the latter is a moral symbol. Archimedes, who defined for us what it is for a line to be straight, considered curved lines of greater mathematical interest.
Postscript: The works of Euclid and Archimedes are available in English translation in inexpensive paperback editions, and they are well worth reading. See your local bookseller.