Hume on the Perception of Causality

94 HUME ON THE PERCEPTION OF CAUSALITY Introduction Few issues in philosophy have generated as much debate and as little agreement as Hume's controversial theory of causality. The theory itself has been notoriously difficult to pin down, and not surprisingly empirical evidence has played a very minor role in the issue of what is meant by 'cause'. This is not, however, due to the fact that empirical tests of the theory are hard to devise, but rather because such tests have usually been undertaken by experimental psychologists addressing slightly different issues and unaware of the philosophical implications of their work. However, recent signs of agreement on the overall nature of the theory (reviewed in Beauchamp and Rosenberg, chapter 1) allow a profitable integration of the theory with psychological research on the nature and importance of the perception of causal relations in conditioning. The significance of some of these experiments will be discussed later, and it will be argued that the factors Hume cited as being the essential determinants of causality, when complemented by the additional factor of the degree of contingency between the cause and the effect, correspond exactly with the factors known to affect conditioning; and therefore, that the laws of conditioning specify the properties that define causal relationships. Hume's Theory of Causality Hume was well aware of the importance of causal connections between events as a source of associations in the mind: 95 'Tis sufficient to observe, that there is no relation, which produces a stronger connexion in the fancy, and makes one idea more readily recall another, than the relation of cause and effect betwixt their objects (T II).2 In other words, if we believe a causal relationship exists between two events, then one of these events, the cause, will readily recall the other, the effect. The problem comes, of course, when we ask how it is that we know that a causal relationship exists. Obviously, a distinction must be made between causation as a physical property and causality as a mental idea. Traditionally, the following definitions have been made: causation is the physical property of one event causing another, such as one ball colliding with and causing the movement of a second ball. This property is part of the realm of mechanics and physics. Causality, on the other hand, describes the attribution by an organism of an effect to a cause. Such a distinction is supported by dictionary definitions. These two ways of thinking of what is meant by the term 'cause' are explicitly discussed by Hume. On the notion of physical causation, he says: We may define a CAUSE to be 'An object precedent and contiguous to another, and where all the objects resembling the former are plac'd in like relations of precedency and contiguity to those objects, that resemble the latter.' Of the mental idea of a causal relationship, on the other hand, he says: A CAUSE is an object precedent and contiguous to another, and so united with it, that the idea of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other. (T 170) Unfortunately, Hume was never less than imprecise in maintaining this dissociation, and often 96 he plainly confused the two definitions. Hence the academic controversy, between those who, like Kemp Smith, believe that the second definition represents a misguided attempt by Hume to analyse the causal relation on a mental level, 3 and those who see both definitions as essential (e.g. Beauchamp and Rosenberg). But surely the first definition simply represents Hume's view of causality as a philosophical relation, while the second represents his view of it as a psychological fact. And it is as much his intention to explain this fact, that ideas do not simply come into our heads for no apparent reason, but on the contrary are summoned up by preceding thoughts which they are associated, as it is to elucidate the philosophical relation. The extent of Hume's commitment to a psychological explanation of causal attribution has been recognised by Beauchamp and Rosenberg: 5 Hume plainly did develop a theory of causal...