II.

Rival Notions

In early modern philosophy, Aristotle's laws of causality were again challenged. The French philosopher and mathematician René Descartes and his school believed that a cause must contain the qualities of the effect or the power to produce the effect. The physical scientists of the 17th and 18th centuries often had a mechanical view of causality, reducing cause to a motion or change followed by other motion or change with a mathematical equality between measures of motion. The British philosopher David Hume carried to a logical conclusion the contention of Sextus Empiricus that causality is not a real relation, but a fiction of the mind. To account for the origin of this fiction Hume used the doctrine of association.

Hume's explanation of cause led the German philosopher Immanuel Kant to posit cause as a fundamental category of understanding. Kant held that the only knowable objective world is the product of a synthetic activity of the mind. He accepted Hume's skeptical result as far as it concerned the world of things. Dissatisfied, however, with the concept that experience is only a succession of perceptions without any discoverable relationship or coherence, Kant decided that causality is one of the principles of coherence obtaining in the world of phenomena, and that it is universally present there because thought, as part of its contribution to the nature of that world, always puts it there.

The British philosopher John Stuart Mill took up the problem at this point. He denied the fundamental postulate of Kant's transcendentalism, namely, that thought is responsible for the order of this world. Mill sought to justify belief in universal causation on empiricist principles; for him, a proposition is meaningful only if it describes what can be experienced.