A concept is not a mere jumble of particulars, – that is only its crudest species. A concept is the living influence upon us of a diagram, or icon, with whose several parts are connected in thought an equal number of feelings or ideas. The law of mind is that feelings and ideas attach themselves in thought so as to form systems. But the icon is not always clearly apprehended. We may not know at all what it is; or we may have learned it by the observation of nature.