Ockham says that when the mind brings forth a concept, it brings forth what would simply be the thing itself, if it had the power to produce it. It would be hard to find a more perfect point of departure to understand thevia moderna.
1.) The concept is now a substitute for the real. According to Ockham, to think of Tibbles the cat means to make something which would simply be a second Tibbles, if my mind were strong enough. The world of knowledge is in every respect a second, substitute world, except for being somehow the product of an inferior maker.
2.) As soon as one makes knowledge a second world whose whole existence consists in being made by us, there is the immediate modern problem of how we are to figure out whether the second world has been made just like the first.
3.) The way that Ockham sees the world of knowledge being made presupposes that our knowledge is always of a singular. St. Thomas, Aristotle, and Plato all denied this saying that intellectual knowledge was never of the singular, at least directly. Ockham’s argument leads to an implicit denial of the difference between sensation an knowledge, which must lead at some point to a denial of all metaphysics. Immortality, the divine existence, causality, the distinction between act an potency, etc. all become impossible to know, despite any claims to the contrary. That Ockham believed that God’s existence could be proven only shows his inability to discern the consequences of his own thought.
4.) The substitute world can only be real, at best, if we establish it on the basis of some test. Thought as such becomes always hypothetical. What is not testable or verifiable can never be considered real.
5.) Words are no longer tools or lights that reveal what is real, they are (again) substitutes for the real. The careful analysis of what is heard about nature is no longer considered relevant. So what if our thought and speech always divides nature and art, sense and intellect, living from dead, quantity from substance, immanence from transitivity? So what! A bunch of scholastic word-games, that’s all. If you want to prove that knowledge and the real correspond, you need tests, not some meditation on words and thoughts about things. You need to see if there is some process by which you can actually prodice something in the real world. Knowledge becomes defined by power to produce.