Mysteries are an affront to reason. One response is to deflate them. In the case of the “eternal mystery” of “the comprehensibility of the world”, such an approach may take the form of collapsing the distance between the comprehending mind and that which it comprehends. That this merely displaces, rather than solves or dissolves, the mystery will become clear; but it is worth dwelling on this way of dealing with Einstein's mystery because it has played an important part in the history of thought and of our sense of who and what we are.

The gap can be closed in either of two ways. According to idealistic philosophy, the comprehended natural world is internal to the mind that comprehends it. I shall examine this view, through its most influential exponent Immanuel Kant, in the present chapter. The opposite view is that our minds are internal to, through being the product of, nature. Our capacity to comprehend the world, the argument goes, is not in the least bit surprising because it is a necessary precondition of the existence and survival of those organisms that have minds. This view, most explicitly developed in evolutionary epistemology, will be the subject of the next chapter. The two approaches can be seen as opposite responses to Plotinus’ luminous question. For idealism, the eye sees the sun because the sun is eye-like; while for naturalistic (materialistic) epistemology eyesight is sun-like, being fashioned out of the same material and subject to the same forces as the sun.

Before I address the first option, the eye-like sun, I need perhaps to defend my choice of philosopher. Why Kant? There are, after all, purer versions of idealism, most notoriously that of George Berkeley the eighteenth-century empiricist philosopher for whom reality consisted solely of minds and their ideas. Such idealism however removes, rather than addresses Einstein's mystery: the comprehended world is dissolved without remainder into the comprehending mind. This generates two problems: the origin of a common world distinct from individual minds (to be solved only by appeal to God-the-Perceiver who upholds such a world); and accommodating the process by which the knowing mind comes to acquire (only) partial and progressive knowledge and understanding of its world.