Impressions and ideas
As an empiricist Hume held that every idea derives from a vivid perception, an impression; to be meaningful an idea must be traced to its impression. He applied this test to the ideas of cause and necessary connection.
Analysing causation
When one billiard ball strikes another, we observe priority in time, contiguity and, over many cases, constant conjunction. No power or necessity in the first ball is ever perceived, and the effect cannot be inferred a priori from the cause: Adam, seeing water for the first time, could not know it might suffocate him.
Necessity from custom
After repeated experience the mind, on seeing A, comes to expect B. Hume located the idea of necessary connection in the inner impression of this customary transition. Necessity lies in the mind, not in objects.
The problem of induction
The assumption that the future will resemble the past cannot be proved by reason, and justifying it by experience is circular, so inductive inference rests on custom rather than reason. This remains a central issue in philosophy of science.
Influence
Kant said Hume woke him from his "dogmatic slumber" and recast causality as a category of the understanding that makes experience possible. Hume's analysis is the starting point for regularity, counterfactual (Lewis) and probabilistic theories of causation.
References
- Hume, D. (1739-40/2000). A Treatise of Human Nature (D. F. Norton & M. J. Norton, Eds.). Oxford University Press.
- Hume, D. (1748/2007). An Enquiry concerning Human Understanding (P. Millican, Ed.). Oxford University Press.
- Beebee, H. (2006). Hume on Causation. Routledge.
- Morris, W. E., & Brown, C. R. (2022). David Hume. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy.