I argued above that we often experience causings in precisely the way David Hume maintained we don’t–I gave the startle reaction as an example.

Let me ladd something still more tendentious. It seems to me that we directly experience causation in sense perception. That is, when I feel a rough surface, sandpaper say, I experience the feeling of roughness as caused by something external to me, the thing that I feel. The experience comes to me as caused by contact with a rough surface. The same goes for most auditory experiences and visual experiences. The visual experience of seeing an automobile bearing down on me comes to me as caused by an approaching object.

This isn’t because of any beliefs I have. From the first, experiences were of causings. It's how sense perception works.
This explains simply why we all believe there is an external world and also why it is a condition of satisfaction of sense experience that sense experience is caused by its object. Just as the experience is a representation of a rough surface, it is a representation of a causing by a rough surface.

Also this helps explain the difference between impressions and ideas. Impressions typically come to us as caused, mere imaginings typically do not. Part of what the empiricists are inchoately gesturing at when they talk about the ‘vivacity’ of impressions is that sense experiences, as opposed to imaginings, are typically experienced as caused. ‘Impressions’ literally come to us, and are experienced as, impressions, that is, effects of external things.

If so, the experience of causation is ubiquitous.