A representation is an object which stands for another, so that an experience of the former affords us a knowledge of the latter. Three things are essential to its existence. In the first place, it must like any other object have qualities independent of its meaning. The printed word ‘man’, for example, consists of three letters, which have certain shapes. It is only through an acquaintance with such distinctive characters that we are able to penetrate to the meaning of a sign. I term such qualities the material qualities of the representation, to distinguish them from those imputed qualities which can only be seen by the mind’s eye. The printed word white is white as to its imputed quality but is materially speaking black or red according to the color of the ink. In the second place, a true representation must have a real connection with its object. If a weathercock indicates the direction of the wind it is because the wind really turns it round. If the portrait of a man of a past generation shows me how he looked, it is because his appearance really determined the appearance of the picture by a train of causation acting through the mind of the artist., If a prediction is trustworthy, it is because those antecedents from which the predicted event follows as a consequence have had a real effect in giving rise to the prediction. In the third place, we cannot call anything a representation which does not appeal to some mind. The idea of the representing object excites in the mind an idea of the represented object, according to some principle of association already established as a habit of that mind.