Kant on Metaphysical Knowledge

What kind of knowledge is metaphysical knowledge?

Synthetic apriori! The most important discovery Kant ever made and the rest of his philosophy depends on it. As much as it is Kant’s most important discovery, it is the most important and most exciting work of epistemology I've ever read. Kant was such a wordy guy, so let’s unpack and see how he got to this conclusion. Kant scholars will correct me where I may be wrong with this. The idea of synthetic apriori knowledge is based on two pairs of distinctions; a distinction between apriori knowledge and empirical knowledge, and a distinction between analytic judgments and synthetic judgments.

1. Apriori knowledge and empirical knowledge

Let's first look at the distinction between apriori and empirical knowledge.

Empirical knowledge

Empirical knowledge is any knowledge that comes from or is justified by appeal to the senses. All kinds of everyday knowledge are examples of empirical knowledge. For example, you know how the weather is like today because you looked out of the window and observed. Your knowledge of the weather depends on the senses. Also, all kinds of scientific knowledge are empirical. So for example, if you are close to the surface of the earth, gravity accelerates objects in free fall at a rate of 9.8 meters per second squared. That’s something we only know because it is backed up by a lot of experimental evidence and the experiments all rely on our senses through observation. 

Apriori knowledge

The opposite of empirical knowledge is apriori knowledge. This is knowledge that isn’t justified by appeal to the senses. For example; think of the truth that all roses are roses. That’s a pretty boring truth because it doesn’t tell us much, but it is true and you know it is true without having to rely on your senses at all because it is true by definition. Math is also apriori because you don’t have to perform any experiment to confirm that 7+5 =12.

Kant further says apriori knowledge has two distinct characteristics: first it is necessary. That is, we don’t think that 7+5 contingently turns out to equal 12. And it is not an accident that 7+5 equals 12. We think it is not possible for 7+5 to equal anything other than 12. In that sense 7+5 necessarily equals 12. Secondly, apriori knowledge is universal. Apriori truths like 7+5 =12 are true without exception. There is no time or place where 7+5 doesn’t equal 12. There is no region of space on the other side where 7+5 =11. These characteristics of apriori knowledge are important because they give us a kind of test or reference to figure out if knowledge is apriori or empirical.

2. Analytic judgments and Synthetic judgments

Now let’s think about the distinction between analytic and synthetic judgments. 

Analytical judgments

An analytic judgement is one in which the concept of the judgment’s predicate is contained in the concept of the judgment’s subject. This means the judgement is true by definition. So for example, consider the judgement “a bachelor is unmarried”. This is analytic because concept “unmarried” is implicitly contained in the concept of “bachelor”. The concept bachelor is made up of the concepts “unmarried” and “man”. The definition of a bachelor is "unmarried man". In the case of the analytic judgement “a bachelor is unmarried”, all the judgement is doing is taking one of the concepts that is already implicitly contained in the concept of "bachelor" and making it explicit. 

Synthetic judgments

Synthetic judgments are the opposite of analytic judgments. Judgments are synthetic when they take the concept of the subject and they connect a new concept to it that wasn’t already implicitly contained in it. They are not true by definition. Take the proposition “a bachelor is miserable”. The concept “miserable” isn’t contained in the concept “bachelor”, it’s not part of the definition “bachelor”. These judgments are ampliative because they actually connect up new information to the judgement’s subject concept that wasn’t already contained in it. In that sense, they actually extend our knowledge beyond what was already contained in the definition of the subject.

Based on the above distinctions, it is really not difficult to come to the conclusion that all analytic judgments are apriori. Because if they are analytic, they are true by definition. Or as Kant relates, “they are true just in virtue of how a judgement’s subject concepts and the predicative concept relate to each other”. But if the judgments are just conceptual or definitional truths, their truthfulness doesn’t depend on experience or the senses, so they are apriori. Consequently, all empirical knowledge is synthetic. Because if it is empirical, the knowledge does depend on experience and the senses. But then the knowledge depends on more than just the definitions of the concepts it involves. So empirical knowledge can’t be analytic and has to be synthetic.

The distinctions overlap each other perfectly, so that really you have one distinction; with analytic judgments and apriori knowledge on one side, and empirical and synthetic judgments on the other side. In this view, analytic judgments make up all the apriori knowledge there is. And empirical knowledge makes up all the synthetic judgments there are. To be more precise, all and only analytic judgments can be apriori and all and only synthetic judgments can be empirical. If that seems right to you, you’re in good company, that’s what most philosophers before Kant thought. David Hume was one who laid out that view especially clearly in his Treatise of human nature. But Kant thinks that Hume is wrong. Kant thinks Hume missed something, that is, synthetic apriori knowledge – which Hume thought was impossible for us to have.

So what’s an example of synthetic apriori knowledge? Kant thought a classic example is math. So for example take a piece of this mathematical knowledge that the interior angles of a triangle sum up to 180 degrees. We can’t justify geometrical truths like this one by conducting experiments or relying on our senses. What’s even more is that truths like this one seem necessary and universal. The interior angles if a triangle add up to 180 degrees without any exceptions. It doesn’t make sense to think there could be a triangle on the other side of the galaxy whose interior angles didn’t sum up to 180 degrees. On the other hand, mathematical truths like this one are synthetic too, Kant thought. The concept of the interior angles of a triangle doesn’t seem to implicitly contain the concept of exactly 180 degrees. At least not in the same simple sense of the concept of a triangle being made up of three sides. The definition of a triangle is a three sided figure enclosed on a plane. But the fact that the triangle’s interior angles sum up to 180 degrees seems to go beyond its definition. It genuinely adds new information not contained in the concept of a triangle. So the truth that the interior angles of a triangle sum to 180 degrees is ampliative, hence synthetic. Kant thought if we do not have the concept of apriori knowledge, there is no way for us to understand the kind of knowledge that math is.

Therefore, metaphysics has to discover truths that are necessary and universal, that is, apriori knowledge, Kant thought. At the same time metaphysics isn’t supposed to be a bunch of empty definitional truths. It should genuinely extend our knowledge beyond definitional truths. Metaphysics is supposed to be ampliative and so has to be synthetic too. Kant thinks this should tell us what kind of knowledge metaphysical knowledge should be.

Why should we concern ourselves with synthetic apriori knowledge?

We know from Descartes meditations that empiric knowledge is knowledge we cannot claim to possess with absolute certainty. On the other hand, a bunch of definitional apriori truths do not get us anywhere because they do not expand our knowledge and understanding of our objective reality, if there is. So, if philosophers are ever going to establish any metaphysical knowledge, it has to be synthetic apriori.