Supposing we tried to constrtuct a mind-model as a result of psychological investigations, a model which, as we should say,
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would explain the action of the mind. This model would be part of a psychological theory in the way in which a mechanical model of the ether can be part of a theory of electricity. (Such a model, by the way, is always part of the symbolism of a theory. Its advantage may be that it is seen at a glance and easily held in the mind. It has been said that a model, in a sense, dresses up the pure theory; that the naked theory is sentences or equations. This must be examined more closely later on.)