A Priori Knowledge
A Priori is a philosophical term that is used in several different ways. The term is suppose to mean knowledge that is gained through deduction, and not through empirical evidence. For instance, if I have two apples now, and I plan to add three apples, I will have five apples. This is knowledge gained deductively. I did not actually need to get the three other apples and place them with the first two to see that I have five. To this extent, the term A Priori is valid.
The problem, though, is that the word is used to describe something entirely different. It is used to describe knowledge that exists without reference to reality. One example is inborn knowledge. Another example often used is mathematics. To understand why this second definition, which is how the term is really used, is flawed, we have to look at exactly what is being said and meant.
Let's look at mathematics. It's easy to see, in the apple example above, that mathematics fits under first, valid meaning of the term. If this were all that was meant by saying that mathematics is a priori, there would be no problem. However, this isn't it. Philosophers then go on to say that mathematics is true without reference to reality. The knowledge of mathematics (as opposed to the knowledge created by mathematics) is a priori. It is known without reference to reality. It is claimed that mathematics is a higher form of knowledge. That even if the world around us doesn't exist, mathematics is still true. That it is a form of knowledge that we can be certain of, even if we deny reality.
How do they make such a statement? First, they see that mathematics is the science of units, and any units are acceptable. I could have said trucks instead of apples above. The validity would be the same. It is true without reference to any unit.
This sounds okay at first. The problem stems from the method of deriving the mathematical abstractions. Teach a child to do simple arithmetic, and you'll recognize that to gain the knowledge of math, one must use some units. Maybe apples. Maybe oranges. It doesn't matter which units. It does matter, though, that some unit is picked. To grasp math, one needs a foundation. Particulars from which an abstraction can be made.
Calling mathematics a priori, or knowledge independent of reality, is to undercut its base. This is the essence of the second meaning of a priori. The meaning that is actually used. An abstraction is made from particulars. Once the abstraction is made, the process from which it was derived is then ignored. The base on which it was built is denied. The abstract knowledge is then said to exist without reference to reality, since the reference is ignored.
In this way, certain kinds of knowledge are said to exist without being dependent on reality. Various explanations for how we are aware of the knowledge are put forward. Some say it is inborn, and we were always aware of it. Others say that although it was inborn, it takes awhile for us to recognize the knowledge. Others decide that it is revelation from some higher power.
The consequences to accepting the claim that knowledge can be a priori is that it leads to faith. When it is suppose that some knowledge exists and is valid without our need of deriving it from reality, it opens the door to pretending all knowledge can be like this. By denying the use of reason to form these abstract ideas, it claims there are alternative methods of gaining knowledge. By severing the tie to reality, it allows any idea to be accepted.