Abstract

Early in his Essays on Intellectual Powers, Reid draws a distinction between mental power, mental operation, and mental capacity (EIP 21). To the untrained eye, these terms could probably be used interchangeably, and Reid believes this is correct, up to a point. He argues that, if we are interested in understanding exactly how the human mind works, we must use these terms with more precise meanings. This is part of his more general strategy of trying to always use the words with their common meanings, as much as possible, but also pointing out that certain philosophical distinctions are needed to carry out the project of laying out the foundations of the science of the mind. This paper explains what the distinction between power, operation, and capacity is, according to Reid, with the goal of understanding why it is important to draw such a distinction, not only for the Reidian project, but for action theory, more generally.