A philosopher, widely read at the present day (Herbert Spencer), describes the mental process which we perform upon perception as follows: "If, when walking through the fields some day in September, you hear a rustle a few yards in advance, and on observing the ditch-side where it occurs, see the herbage agitated, you will probably turn towards the spot to learn by what this sound and motion are produced. As you approach there flutters into the ditch a partridge; on seeing which your curiosity is satisfied--you have what you call an explanation of the appearances. The explanation, mark, amounts to this--that whereas throughout life you have had countless experiences of disturbance among small stationary bodies, accompanying the movement of other bodies among them, and have generalised the relation between such disturbances and such movements, you consider this particular disturbance explained on finding it to present an instance of the like relation" (First Principles, Part I, par. 23). A closer analysis leads to a very different description from that here given. When I hear a noise, my first demand is for the concept which fits this percept. Without this concept, the noise is to me a mere noise. Whoever does not reflect further, hears just the noise and is satisfied with that. But my thought makes it clear to me that the noise is to be regarded as an effect. Thus it is only when I combine the concept of effect with the percept of a noise that I am led to go beyond the particular percept and seek for its cause. The concept of "effect" calls up that of "cause," and my next step is to look for the agent, which I find, say, in a partridge. But these concepts, cause and effect, can never be gained through mere perception, however many instances we bring under review. Perception evokes thought, and it is this which shows me how to link separate experiences together. If one demands of a "strictly objective science" that it should take its data from perception alone, one must demand also that it abandon all thought. For thought, by its very nature, transcends the objects of perception.