Locke thought properties are of two basic kinds.
Some properties are primary, such as mathematical, mechanical, object dimensions, object weight, etc., while other qualities are secondary including things such as smells and tastes.
These secondary qualities depend on the observer, or are mind dependent.
In addition, Locke was unsure that there is just mind and matter in the world. He believed there existed another category of reality, but he wasn't sure.
He is ready to accept the possibility that there is no Cartesian soul, no immaterial and immortal soul.
He has an excellent argument in which he advanced his opinion regarding this matter.
He proposed of human beings that one of two things must be true.
Either humans are material objects that think and have emotions or there must be something immaterial in us that thinks and has emotions, that is mysteriously allied to the material body.
Both of these possibilities are unintelligible and yet, Locked proposed, one of them must be true. He concluded that Cartesian Dualism is probably true but we cannot know this for sure.
