What does Spinoza mean by truth? When we think about truth normally in philosophy then we think about the agreement between a statement and a state of affairs in the world, but this can’t be what Spinoza means by truth, at least not in any simply way. Why is this? Because for Spinoza truth cannot be the agreement between two different attributes, since attributes can have no causal relation to one another. Thus the idea of ‘tree’ cannot be true because it agrees with an object called a ‘tree’, rather an idea is true because it is true in itself and not because it ‘represents’ something else. What then does it mean to say that an idea is true in itself?
In one sense, Spinoza is repeating the story of truth that we have heard since Plato: perception is not sufficient to explain truth. This is because, as we know, perception does not tell me truth about things at all. Indeed if all I had were perceptions, then I probably wouldn’t have a very good idea of reality at all. One of the basis premises of the new modern science is what common sense tells us about nature (which we might say is the Aristotelian starting point) can only lead us astray. Common sense might tell me that the earth is at the centre of the universe, because that is how it appears to me, but I know in fact that this is not the case. What is true is not what my senses tell me, but what true knowledge does, and true knowledge is not perception, as Plato would have already told us, but mathematics. Copernicus does not disagree with Ptolemy because he saw something different in the heavens, but he postulated a different mathematical model and that is why he saw the heavens in a different way. It might be the case that Galileo did see something different in his telescope, but he wouldn’t have seen what he was looking for unless he had already agreed with Copernicus’s mathematical revolution.
If an idea is not true because it agrees with what I see with my eyes, then why is it true? Here we have to make a difference between the psychological event of having an idea and the content of the idea itself. I might be thinking of a circle because I see a circle. Or I might be thinking of circle because I associate it with something else. Perhaps I have being thinking about bears and then the idea ‘circle’ just pops in my mind. Or, I might be thinking about circle, but I have completely the wrong idea of circle in my mind. I might think lines drawn from the centre of the circle are not equal. None of the instances of thinking of the idea circle would make the idea true. The occasion of thinking the idea does not make the idea true (and this is really the reason why perception cannot be the source of the truth of ideas, since it psychologises them, and would make truth subjective). What is true is the objective content of the idea itself, which can be thought by anyone (or anything if it capable of thinking true ideas).
In proposition 35 of the second part of the Ethics, Spinoza explains how such an error is possible. There is no positive idea of falsehood. Strictly speaking there are no false ideas in themselves, because every idea is an idea of something that exists. Rather there are confused ideas. To have an ignorant idea is to have an idea of a positive thing, but in a confused way. The example that Spinoza gives in the scholium is the idea of freedom. Why is it that people falsely believe they are free? The answer is because they are ignorant of the causes that make them act the way they do. Because they are ignorant, they therefore think they are free. The cause of false ideas is not a real idea, but ignorance on our behalf, and this ignorance is always ignorance about causes. To use the other example that Spinoza gives in this scholium. I believe that the sun is 200 hundred feet away from me because I am ignorant of the true distance. Even though I know that the sun is further away than it seems. Because the distance that it appears from me is caused by the relation of my body to the sun, I might still fall under the error that the sun is closer than the actual distance. Of course I can also understand why it is that the sun appears in the way it does to me (I can understand for example that the sun really doesn’t get larger at sunset or change from yellow to red, but this is the effect of light in the Earth’s atmosphere), but that means I have to have a true idea of what the sun is and what the my body is and how they interact.
Because of our limited knowledge, Spinoza thinks that is very easy for us to have inadequate of idea of things, but does he think that we can have adequate idea? It would surprise us if he said ‘no’ to this questions, since Spinoza is an exponent of the new modern science. He is a realist. He does not think that our scientific theories are just our way of understanding what reality is, but are true picture of what is. Indeed Newton’s laws would be true, even if there were no human being to think them.
The difference is between understanding a particular thing as a mode or as an expression of substance. Let say I look at a stretch of water that is in front of me. I could just describe the water as I see it, perhaps in the way that I writer might describe it in a story, or painter paint it. Or I could describe it in terms of substance. Not just this stretch of water in front of me, but through an attribute that expresses not just this part of reality, but the whole of reality. Isn’t this just what science does? Science does not explain this or that particular instance or occasion of water, but the reality of water as such, which for Spinoza would be explained in the current scientific explanation of nature through the general laws of physics. This would be to have an adequate, as opposed to an inadequate understanding of water, because I would be understanding its true cause, which is substance explained in this case through the attribute extension.
The laws of physics are what Spinoza calls ‘common notions’. The occasion for us to have ideas is our bodies, for this nothing in our minds that does not come via our bodies. Thus if we didn’t have eyes to see the sun, then we wouldn’t have the idea of sun. The error, then is not think that the ‘truth’ of the idea of the sun somehow has its origin in us. We can think the true idea of the sun, because the true idea of the sun corresponds (or is the same as) as the causal relation between the mode and substance. There cannot be any other idea of the sun that is true because nature cannot be any different than what it is, otherwise substance would be lacking that different reality and therefore would not be infinite.
How can we escape the confused ideas of the realm of sensations and affections? We can only do so when we understand ideas internally and not externally. To understand ideas internally means to know the necessary order and connections of ideas themselves and not how they are encountered through affections. Yet even though I might know the difference between the two, how do I take the step from one to the other? It is probably wrong to say that Spinoza rejects imagination, because this would be argue that he rejects the body, but as we know, for Spinoza, only through the body can I know the world. There must then be a route from inadequate to adequate knowledge, and the key is ‘common notions’.
Inadequate knowledge only tells me about my individual encounters with things. What Spinoza calls duration. How something appears to me at a certain time and place, and which I might subsequently remember and associate with other things. But I can, through duration, leap out of duration. I can recognise what is ‘common to all things’. In so doing, I am understanding the mode through substance and not through another modes, which I can only have a limited knowledge of. It is possible to understand the causal relation between substance and modes. It is not possible to understand the infinite causal relation between modes (it is this inadequate understanding we have seen, for example, that produces the error of free will).
It is very important not to confuse common notions with universals. In IIP40S1, Spinoza disputes the existence of universals precisely because they are not common notions. I can have an adequate idea of scientific laws of nature that are common to all bodies, but what I cannot have is the idea of all horses that would be common to the universal ‘Horse’. The latter is merely a word, whereas the former is a true idea. This is why we differ in what we mean by the word ‘horse’, but we do not differ when we understand what is common to all things (like extension and the laws of nature that follow immediately from it), because this is common to nature as such, and not just a use of words. When we understand the universe, we understand it as it is in reality, and our understanding cannot be any different from God’s (what the universe is in reality in terms of truth), because there couldn’t be any other understanding. There is no mysterious transcendent cause, nor any distinctive human understanding (as there is in Kant for example) that would be any different from truth of what is actually in reality, which would be true whether we knew it or not.
It is possible to have adequate ideas because it is possible to know the causes of things. Of course as finite beings, it is not possible to for us to know the cause of everything, but that does not mean that we know nothing. It is possible for us to understand the essence of God for example, for Spinoza. It is possible for us to understand the idea of a triangle, though it is not possible for us to have the idea of every triangle that has ever existed. To have an adequate idea is to understand something through its cause rather than its effects. Thus to have an adequate idea of the sun is to understanding why it makes my skin feels warm and appears closer than it is in reality, as opposed to an inadequate idea, which starts with effects, my warm skin, the appearance of the sun and the sky, and argues backwards towards the cause. The sun is close to me in the sky because it is circling the earth; the sun warms the my skin because it was created by God to benefit human beings. Both these arguments are false because they argue from effects rather than causes. To understand the effects of the sun through its cause is to follow the order of reality itself. It is to go from substance as it expressed through its attributes and then to modes. Rather than to start with modes and to try and get back to attributes and from there to substance.
We have only distinguished between inadequate and adequate knowledge in this lecture, but there is third level of knowledge that Spinoza describes in IIP40S2, which he calls ‘intuitive’. We will have to wait to Part 5 of the Ethics to find out what this.