Now if I can show that even if one concedes all objective validity to this cardinal proposition of the rational doctrine of the soul (that everything which thinks is a simple substance) in its pure signifi cance as a merely rational judgment (from pure categories), neverthe less not the least use of this proposition can be made in respect of its dissimilarity to or affinity with matter, then this would be the same as if I had consigned this supposed psychological insight to the field of mere ideas, which lack the reality of an objective use.