Usually used to mean denying the possibility of knowing the nature or existence of God, but used by Marxists with the meaning of denying the possibility of knowledge of the objective world. Agnosticism is an extension of Skepticism in that while skepticism is always a valid aspect of investigation, Agnosticism elevates this doubt into an absolute denial of the possibility of knowledge. The term was coined by the British natural scientist Thomas Huxley and could be used to encompass the philosophy of Hume, Kant, neo-Positivism and others.