Thothistox said:
Hume was speaking in very strict terms. I'm sure that he accepted causality as a useful myth in an everyday context. For example, I doubt anyone would claim that we should stop researching medicines because we cannot establish a strict causation between them and the ailments they purportedly assuage.
Well, here is Hume's view:
Hume was an empiricist, who believed that all our concepts (he called them 'ideas') are derived from impressions given in experience. He discussed several concepts, one of them a concept of causation, and how we acquire this concept. It was a common belief that causation is a feature of the world, that things cause other things to happen, that stones break windows, and such, and that we can actually observe one event causing another. Also this concept involves a necessary connection between causes and effects, that causes necessitate their effects.
What Hume claimed is that we can never observe any necessary connections in the world, we only observe regularities, some events always follow other events. But there is nothing we observe in nature can ever tell us that something is a cause, and something is an effect. Consider two cases: (1) billiard ball A hits a billiard ball B, and B starts to move, and (2) ball A touches B, but B starts to move not because A hits it, but because there is a small motor inside. If the timing is just right, the second case would look exactly like the first. There will be no difference with impressions, and we won't be able to discern a causal difference - B moving because it was hit, or because it has a motor inside it.
So we do not get any impressions of necessity and necessary connection between events from the events themselves. Still, there should be some impressions we derive this concept, and he claims that this impression comes from our minds. After observing things happening many times, we form a habit of expecting this pattern to continue. This impression of necessity is a work of imagination.
In essence, Hume talks about our concepts, and not about causation itself. May be there are necessary connections between events in the world (realism about causation), but they are unobservable. For a realist about causation, causation is not just a useful fiction. In any case, it is fair to say that we can't observe any causation directly, and have to infer causal relations based on correlations we observe. That's what science is doing. The same observations may be interpreted in many ways, positing very different unobservable theoretical entities. But it is probably one of the areas we simply can't have a complete certainty.
Obviously, people shouldn't stop research just because philosophers have no frigging idea about a lot of things, especially concerning science. Science seems to work just fine and make our lives better. Still for a scientist it would be good to study some philosophy of science, in order to be aware of limitations and problems in an attempt to provide rational foundation for it.