A good example as to why causation isn't always connected is found on page 420. Hume asserts that only when two objects are "constantly conjoined" can observers "infer the one from the other." But rarely are two effects and two causes connected, Hume continues. If a cause and effect have "resemblance" to another cause and effect, they can be conjoined, but that is rare indeed.

Put into simpler words, Hume doubts that even with a repetition of conjunctions it would be safe to believe a "connection" between the cause and effect would be established. Indeed, after a person experiences sees instances repeated repetitiously, the mind is convinced through the person's habits and reflections that upon the introduction of one event, another event is expected to happen, and humans believe this will happen. His own explanation is that a cause is an "…object followed by another, and whose appearance always conveys the thought to that other"; but, as earlier noted, this situation does not necessarily imply a connection.

Hume's metaphysics of perception (impressions, ideas, simple and complex ones).

Perceptions, Hume believes, are independent:

"Now as every perception is distinguishable from another, and may be considered as separately existent; It evidently follows, that there is no absurdity in separating

any particular perception from the mind…that is, in breaking off all its relations with that connected mass of perceptions which constitute a thinking being"

(Treatise, 207).

What he is getting at here regarding perception (on page 207 of his Treatise) is that the mind is "…nothing but a heap...

On page 202 of his Treatise, he distinguishes between perceptions that are dependent on the mind, and the objects that created the perception which are not dependent on the mind's ability to perceive:
"In order, therefore, to accommodate myself to their notions, I shall at first suppose; that there is only a single existence, which I shall call indifferently object or perception, according as it shall seem best to suit my purpose, understanding by both of them what any common man means by a hat, or shoe, or stone, or any other impression, covey'd to him by his senses.

I shall be sure to give warning when I return to a more philosophical way of speaking and thinking" (Hume, Treatise, 202).

What is germane to his argument here is that the hat, shoe, and stone always exist whether the person perceives them or not. So that in a way flies in the face of his theory that perceptions are free floating out there, tethered to nothing. Scholars argue that perceptions do in fact actually need substance -- otherwise there cannot be perceptions (i.e., perceiving something out of whole cloth is simply fantasizing, not perceiving; that is what scholars argue in rebutting Hume's viewpoint on perceptions).

But notwithstanding the contrarian viewpoints vis-a-vis Hume's approach to perceptions, he believes perceptions "…may exist separately, and have no need of anything else to support their existence" (Treatise, 233). Basically the philosopher's point is this: if humans' perceptions are different,