Your Mind and How to Use It: A Manual of Practical Psychology

Mind is defined as "the faculty or power whereby thinking creatures, feel, think, and will." This definition is inadequate and circular in nature, but this is unavoidable, for mind can be defined only in its own terms and only by reference to its own processes. Mind, except in reference to its own activities, cannot be defined or conceived. It is known to itself only through its activities. Mind without mental states is a mere abstraction—a word without a corresponding mental image or concept.