From the methodological standpoint, however, we see that 'mechanism' and 'vitalism' by no means form the mutually exclusive disjunction they have been supposed to do. If a 'non-mechanist' wishes to deny the assumption of methodological mechanism that biological explanations must also be physico-chemical ones, it is obviously by no means intended that the required explanation must be 'vitalistic', i. e. involving the assumption that in living organisms factors analogous to psychical ones are 'at work'. A 'non-mechanistic' theory which is not all 'vitalistic' thus appears to be logically possible, and if we make a critical study of mechanism and vitalism this possibility will be seen to be of special importance.

p. 29 - Modern Theory of Development, 1933, 1962