We may therefore now say that, on Hume’s account, to invoke causality is to invoke a constant conjunction of relata whose conjunction carries with it a necessary connection. Thus, objections like: Under a Humean account, the toddler who burned his hand would not fear the flame after only one such occurrence because he has not experienced a constant conjunction, are unfair to Hume, as the toddler would have had thousands of experiences of the principle that like causes like, and could thus employ resemblance to reach the conclusion to fear the flame. But Hume is at pains to point out that the definitions are inadequate. Though this treatment of literature considering the definitions as meaningfully nonequivalent has been brief, it does serve to show that the definitions need not be forced together. There are reams of literature addressing whether these two definitions are the same and, if not, to which of them Hume gives primacy. One alternative to fitting the definitions lies in the possibility that they are doing two separate things, and it might therefore be inappropriate to reduce one to the other or claim that one is more significant than the other. Some scholars have argued for ways of squaring the two definitions (Don Garrett, for instance, argues that the two are equivalent if they are both read objectively or both read subjectively), while others have given reason to think that seeking to fit or eliminate definitions may be a misguided project.

Having approached Hume’s account of causality by this route, we are now in a position to see where Hume’s two definitions of causation given in the Treatise come from. Yet given these definitions, what is billiards it seems clear that reasoning concerning causation always invokes matters of fact. Matters of fact, however, can be denied coherently, and they cannot be known independently of experience. As we experience enough cases of a particular constant conjunction, our minds begin to pass a natural determination from cause to effect, adding a little more "oomph" to the prediction of the effect every time, a growing certitude that the effect will follow again. In fact, later in the Treatise, Hume states that necessity is defined by both, either as the constant conjunction or as the mental inference, that they are two different senses of necessity, and Hume, at various points, identifies both as the essence of connection or power. Ergo, the idea of necessity that supplements constant conjunction is a psychological projection.

Because of this, our notion of causal law seems to be a mere presentiment that the constant conjunction will continue to be constant, some certainty that this mysterious union will persist. Once more, all we can come up with is an experienced constant conjunction. Nevertheless, ‘causation’ carries a stronger connotation than this, for constant conjunction can be accidental and therefore doesn’t get us the necessary connection that gives the relation of cause and effect its predictive ability. There is nothing in the cause that will ever imply the effect in an experiential vacuum. Hume argues that we cannot conceive of any other connection between cause and effect, because there simply is no other impression to which our idea may be traced. For instance, a horror movie may show the conceivability of decapitation not causing the cessation of animation in a human body. Hume challenges us to consider any one event and meditate on it; for instance, a billiard ball striking another. As causation, at base, involves only matters of fact, Hume once again challenges us to consider what we can know of the constituent impressions of causation.

In both the Treatise and the Enquiry, we find Hume’s Fork, his bifurcation of all possible objects of knowledge into relations of ideas and matters of fact. Therefore, knowledge of the PUN must be a matter of fact. It alone allows us to go beyond what is immediately present to the senses and, along with perception and memory, is responsible for all our knowledge of the world. We use knowledge of (B) as a justification for our knowledge of (B). Start by using an orange marker to color small foam balls orange, and then, imitating the pattern of a pumpkin's lines, wrapping thin strips of black, adhesive-backed hook-and-loop tape (use the scratchy side) around the ball. The use of brushless motors in these gimbals ensures efficient operation, allowing for seamless pan, tilt, and roll axis movements. This is the yaw axis. However, Blackburn has the first as giving the "contribution of the world" and the latter giving the "functional difference in the mind that apprehends the regularity." (Blackburn 2007: 107) However, this is not the only way to grant a nonequivalence without establishing the primacy of one over the other.