s1 is a concept of dualism/an idea that the fundamental part of existence f1 differs/is distinct from/contrasts with/is unlike the other fundamental part of existence f2 in property/dimension/quantity f3, by thinker s2.
Mind-body or mind-matter dualism (e.g. Cartesian Dualism) or physical dualism (e.g. the Chinese Yin and Yang)and others.