In his Gifford Lectures, Mitchell’s aim is to understand the place and the power of minds in nature, as neither can be had without the other. Mind is discovered in just the same way as nature is. The surface of phenomena explains itself but not the depths of nature itself, just as the subject’s knowledge of qualities and faculties does not include knowledge of the brain. They are simply the surface of mind.

The introduction concerns itself with the three places of the mind: in nature, in the head, and in ‘the mind’s own place’. Analogies between the mental and the physical life are suggested, but the analogies are either too narrow or too abstract. The narrow readings create gulfs between the knower and the known, and while the abstract readings leave some of these gulfs empty, they fail to make proper distinctions and do not escape the gulfs. These failures define the demand for deeper analysis and an understanding of the living line between minds and nature.

Part I consists of four sections exploring the surface gulfs, the practical gulfs and our reluctance to leave them behind. The first surface gulf is between phenomena and nature, and Mitchell asks how the phenomena can lead us to the roots of nature. Then there is the space gulf between minds and nature. Attempts to close it can end in the confusion of the living line and the correlation line between structures of mind and structures of nature. The third gulf concerns the mind as it is in nature, the laws of thought as laws of nature. How can we conceive of reason in nature? If the mind makes objects its causes, then causes are reasons. If this closes the theoretical gulf between life and reason, the practical gulf appears: the power of objects in controlling belief and the reality of the fundamental cause in mental rehearsals. Mitchell concludes Part I with an appreciation of our reluctance to leave the gulfs, because physical elements will never be seen to compound themselves into a sensation, nor physical structure into mental, yet sensation is a product of physical conditions. But here nature is closed too soon, and the existence of the gulfs reveals a neglect of the relation of minds to nature.

Part II considers a mind’s own place in respect to the origin of the object, the service of minds to nature and the mental surface. Thought is defined as consciousness of an object, though there are many different kinds of objects and thus ways in which objects can be known by thought. The simple objects of sense are the first to become objects; our organs are such that simple ideas are established first so that we can attend to the more complex. The projection of sensory complexes includes the projection of space and time. This fact about minds tells us that real objects must have a suitable essence in order to fit minds and be felt. Thought handles things as they were, are and will be. A true idea and a false one about yesterday certainly feel the same, yet there is no doubt that one can be in error about the past. Objects exist without minds, and yet they answer the question of the place of minds. The felt object is the fundamental cause of the mental surface, but beneath this lie the means in the objects and subjects themselves.

In Part III, Mitchell looks from the surface to the depth in nature. Laws and theories develop through logical and physical analysis, and the analysis always begins with the surface. We proceed from what is first for us, and go by degrees to what is first for nature. Yet this road can become blocked if we cannot move beyond conceiving the objects of sense to be a model for the stimuli. Certain basic theories of gases failed in this way and required radiation theory, with notions of wave, particle and quanta that went beyond the sensible or imaginable, before barriers to knowledge could be overcome. Theories are organs related to understanding as eyes are to seeing, and yet they are related to nature as eyes are to light. The relation of theory to nature then is not one of likeness but of articulation. Theories do not reduce to statements about phenomena as phenomena need not always keep theory in control, and theory need not account for all phenomena.

In his lecture the ‘Rigid and Flexible’, Mitchell relates the development of quantum theory in its advance from the classical system to the understanding of mind in nature. Our organs work so that we can comprehend and articulate nature, but they never ask nature to subject itself to them. It is the continuity from eye to theory that forms the theatre from which we see the play of nature, and it is always this that must make shift to conform; concepts and theories are inventions, but some are successful discoveries. Quantum theory finds nature to be more responsible for our grasp than classical theory allows.

Quantum theory and the principle of general relativity bring about a reversal. The projections from surface to depth, which began as analogies, lead the way into analyses, until the properties thought worthiest of being final gave way. The surface characters of nature, which at the beginning looked unworthy of depth, are found to be fundamental. Nature proves itself intelligible in the way that it is sensible; from containing, it has gone on to prove that it is nothing besides the system of phenomena. Real nature, for Mitchell, holds phenomena in the way that space-time holds space and time, which are its phenomena. The evolution of mental life and that alone advances nature to a world of objects and their power. Mitchell returns to the thought with which he began his enquiry: that a growing thing is known from what it grows to.