But in order that this value of theirs may become effectual, a certain state is necessary in the recipient of it. The digesting, the breathing, and perceiving functions must be perfect in the human creature before the food, air, or flowers can become their full value to it. The production of effectual value, therefore, always involves two needs; first, the production of a thing essentially useful; then the production of the capacity to use it. Where the intrinsic value and acceptant capacity come together there is EFFECTUAL value, or wealth. Where there is either no intrinsic value, or no acceptant capacity, there is no effectual value; that is to say, no wealth. A horse is no wealth to us if we cannot ride, nor a picture if we cannot see, nor can any noble thing be wealth, except to a noble person. As the aptness of the user increases, the effectual value of the thing used increases; and in its entirety can co-exist only with perfect skill of use, or harmony of nature. The effectual value of a given quantity of any commodity existing in the world at any moment is therefore a mathematical function of the capacity existing in the human race to enjoy it. Let its intrinsic value be represented by _x_, and the recipient faculty by _y_; its effectual value is _x y_, in which the sum varies as either co-efficient varies, is increased by either's increase,[68] and cancelled by either's absence. [68] With this somewhat strange and ungeometrical limitation, however, which, here expressed for the moment in the briefest terms, we must afterwards trace in detail--that _x y_ may be indefinitely increased by the increase of _y_ only; but not by the increase of _x_, unless _y_ increases also in a fixed proportion. Valuable material things may be conveniently referred to five heads:-- 1. Land, with an associated air, water, and organisms. 2. Houses, furniture, and instruments. 3. Stored or prepared food and medicine, and articles of bodily luxury, including clothing. 4. Books. 5. Works of art. We shall enter into separate inquiry as to the conditions of value under each of these heads. The following sketch of the entire subject may be useful for future reference:-- 1. Land. Its value is twofold-- A. As producing food and mechanical power. B. As an object of sight and thought, producing intellectual power.