 Lewis (1929, 37–8) believed that, on reflection and analysis, we can distinguish three elements in perceptual knowledge: (1) the given or immediate data of sense, (2) the act of interpreting the given as an experience of one sort of thing as opposed to another, and (3) the concept by which we so interpret the given by relating it to other possibilities of experience. Our experience of the real is not given to us in experience but is constructed by us from the data of sense through acts of interpretation. When I know that I am looking at a table and reflect on my experience, I realize, on analysis, that there are certain highly specific sensuous qualities presented to me that I am immediately aware of. Moreover, I realize that, in the light of this and other experiences I recall, I expect, with some likelihood, I would have certain other experiences, e.g. of feeling something apparently hard, were I to have the experience of performing certain acts, e.g. of reaching out with my hand. In doing so, it is the concept of seeing a table that I am applying to my experience rather than that of seeing a horse or that of hallucinating a table, either of which would have involved different expectations of experience consequent upon action. Only an active being can therefore have knowledge, and the principal function of empirical knowledge “is that of an instrument enabling transition from the actual present to a future which is desired and which the present is believed to signalize” (Lewis 1946, 4).