Concretism may be understood as follows:
Concretism is a concept which falls under the more general concept of participation mystique. Just as the latter represents a fusion of the individual with external objects, concretism represents a fusion of thinking and feeling with sensation, so that the object of one is at the same time the object of the other. This fusion prevents any differentiation of thinking and feeling and keeps them both within the sphere of sensation; they remain its servants and can never be developed into pure functions
CW6 ¶ 698MAGICAL EFFECT
Concretism, therefore, is an archaism. The magical influence of the fetish is not experienced as a subjective state of feeling, but sensed as a magical effect. That is concretistic feeling. The primitive does not experience the idea of divinity as a subjective content; for him the sacred tree is the abode of the god, or even the god himself. That is concretistic thinking. In civilized man, concretistic thinking consists in the inability to conceive of anything except immediately obvious facts transmitted by the senses, or in the inability to discriminate between subjective feeling and the sensed object
CW6 ¶ 697