1. Let us begin with the problem of the mystery of all existence, and see whether it remains unaffected, or whether it disappears in face of naturalistic interpretation, with its discovery and formulation of law and order, with its methods of measuring and computing. More primary even than faith and heartfelt trust in everlasting wisdom and purposeful Providence there is piety; there is devout sense of awe before the marvellous and mysterious, before the depth and the hidden nature of all things and all being, before unspeakable mysteries over which we hover, and abysmal depths over which we are borne. In a world which had not these, and could not be first felt in this way, religion could not live at all. It could not sail on its too shallow waters, or breathe its too thin air. It is indeed a fact that what alone we can fitly speak of and love as religion—the sense of mystery and the gentle shuddering of piety before the depth of phenomena and their everlasting divine abysses,—has its true place and kingdom in the world of mind and history, with its experiences, riddles, and depths. But mystery is to be found in the world of nature as well. It is only to a very superficial study that it could appear as though nature were, or ever could become, plain and obvious, as if the veil of Isis which shrouds its depths from all investigation could ever be torn away. From this point of view it would make no difference even though the attempt to range the whole realm of nature under the sway of inviolable laws were to be immediately successful. This is expressed in the first of our main propositions (p. 35). In order to realise this it is necessary to reflect for a little on the relation of “explanation” and “description” to one another, and on what is meant by “establishing laws” and “understanding” in general. The aim of all investigation is to understand the world. To understand it obviously means something more than merely to know it. It is not enough for us to know things, that is, to know what, how many, and what different kinds of things there are. On the contrary, we want to understand them, to know how they came to be as they are, and why they are precisely as they are. The first step towards this understanding is merely to know, that is, we must rightly apprehend and disentangle the things and processes of the world, grouping them, and describing them adequately and exhaustively.