With the advent of modern science in the 17th century, thinkers such as Rene Descartes and Galileo Galilei rejected some of Aristotle's explanatory principles and made the efficient cause the central concern of scientific reasoning. Descartes believed that the efficient cause had to contain either the features of the effect or have the power to produce them. In the 18th century, David Hume gave the most careful and influential examination of the causal relation. He claimed that no deductive relation exists between the cause and the effect and that no necessary connection between them is observable. Thus, Hume said, causal reasoning is merely the expectation that constantly conjoined events will remain so in the future.
People have no way of telling why events are so conjoined.
Immanuel Kant was influenced by Hume and claimed that causality is one of the categories used to classify experience, but that people do not find it in experience. Hume's analysis of causality, in a more refined form, has become the standard explanation of the causal relationship among most philosophers of science and among many scientists.