The long eighteenth century was the period in Britain and Western Europe when the mind came into its own. Thought – including progress in science and medicine and in the understanding of the mind itself – was at last, after the religious and civic turmoils of the seventeenth century, deriving the full benefit of those decisive breaks with the past that had occurred during the European Renaissance. Increasingly liberated from the remaining pockets of medievalism, such as humoral theory in understanding the body, and from strict religious oversight of what might be thought and written, scientists were able, probably for the first time, to give full rein to those fundamentals of modern science, free thought and factual observation. William Harvey, early in the seventeenth century, identified and demonstrated the circulation of the blood; Isaac Newton, half a century later, discovered the movements and orbits of lunar and planetary bodies. In the same way, the celebrated physician Thomas Willis argued in his Cerebri anatome (1664) that the human brain operated through a series of nervous impulses and reactions, basing his conclusions on clinical observation and experiment. The whole human organism was being recognized as more dynamic, more mechanical, and far more surprising than earlier generations of scientists had dared to think, and the most exciting faculty of all in the new body was the mind itself. There was more to thought, it began to appear, than we thought.

Philosophy and the mind

While some were observing the brain and the nervous system, other thinkers and medical men were turning their attention to issues concerning the mind – to what was being thought and why. Here the key figure was John Locke, the philosopher and physician. An Essay concerning Human Understanding (1690) was probably the single most influential philosophical work upon the study of mind for the century that followed (see chapter 33, “Philosophy”). By denying the existence of innate ideas and deriving all knowledge from sense or sensation, Locke separated thought from any residual traces of what might have been a divine template, and positioned it instead firmly within the individual organism, its species characteristics, and its distinctive quirks and malfunctions. In doing so, he set the agenda for attitudes towards issues of identity, of mental normality and abnormality, of popular as well as philosophical understanding of sanity and insanity, and of education for a chain of thinkers who followed.