One of the theories defined in James Baldwin's Dictionary of Philosophy and Psychology, published in 1901, is "The Double Aspect Theory". It is "the theory of the relation of mind and body, which teaches that mental and bodily facts are parallel manifestations of a single underlying reality". It "professes to overcome the onesidedness of materialism and idealism by regarding both series as only different aspects of the same reality, like the convex and the concave views of a curve; or according to another favourite metaphor, the bodily and the mental facts are really the same facts expressed in different language".