A representation is an object which stands for another so that an experience of the former affords us a knowledge of the latter. There are three essential conditions to which every representation must conform. It must in the first place like any other object have qualities independent of its meaning. It is only through a knowledge of these that we acquire any information concerning the object it represents. Thus, the word ‘man’ as printed, has three letters; these letters have certain shapes, and are black. I term such characters, the material qualities of the representation. In the 2nd place a representation must have a real causal 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 tells 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 painter. If a prediction is trustworthy it is because those antecedents of which the predicted event is the necessary consequence had a real effect in producing the prediction. In the third place, every representation addresses itself to a mind. It is only in so far as it does this that it is a representation. The idea of the representation itself excites in the mind another idea and in order that it may do this it is necessary that some principle of association between the two ideas should already be established in that mind. These three conditions serve to define the nature of a representation.
Every idea is a representation.