The advantages of basing the interpretation of mental factors on a model which is related to the possible physiological structure of the brain are re‐emphasized. The importance of the concept of determinacy of factors for those who claim that factors exist in some more or less permanent sense is pointed out, while the fact that good determinacy is seldom achieved is taken to counter‐indicate permanency. Examples are given to support the arguments, and it is shown that the value of factor analysis as a statistical aid is little affected when the notion of factors as entities is discar