2. Permanent and stable cases; to be met with everywhere, because involved in the structure of the human mind. They are fixed in language. When dealing with the expression of the emotions (Chap. IX.) we met with “the principle of association of analogous sensations,” formulated by Wundt. Adapting it to our present subject, we may say that sensations imbued with a similar emotional colouring are easily associated, and strengthen each other. Nothing can differ more in nature than our external sensations (except smell and taste), and the qualities which they make known to us; the data of sight and hearing have no resemblance to one another as cognitions of the external world, yet we speak of sombre voices, clear voices, screaming colours, coloured music. We associate sight with thermal sensations, as when we speak of warm or cold colours. Taste also has its share—bitter reproaches, subacid criticism. Finally, touch, as Sully-Prudhomme has remarked, is perhaps the most abundant source of associations between the idea of the physical sensation and an emotional state; compare the terms touching, hard, tender, heavy, firm, solid, harsh, penetrating, poignant, piquant, etc. At the bottom of all these associations there is a common emotional colouring which both causes and supports them. Perhaps it would be more accurate to class them among the cases of semi-conscious emotional influence; but we have already said that our division into conscious and unconscious factors is superficial and of no great importance.