Locke Book I- No innate speculative principles

Locke is writing as one of the most proiminent and foundational empiricists in modern philosophy. The main doctine of empiricism is that there is nothing in the intellect which was not first in the sense (see Sextus Empiricus). So one of the first things Locke must do to present his argument is to demonstrate that there is no such thing as innate ideas, the doctrine of innate ideas being one which many rationalists and idealists in philosophy hold dear. Descartes was one of the major proponents of innateness in Locke's time, defending the case of the idea of God being innate and a "clear and distinct" idea. Locke is out to prove him wrong. He begins by taking what most proponents of innateness take to be one of the most fundamental innate ideas, namely that it is impossible for a thing to be and to not be (see the logical law of non contradiction). The proponents of innateness use the argument that something can be proved innate if it is universally consented to, that is, if it is something which everyone can agree on. Locke destroys the idea of universal consent in that it cannot be found for any idea, no matter how seemingly foundational, and that even if it were the case that something was universally consented to, it would not prove something innate. The problem for innateness is that in order for someone to consent to the validity of a proposition such as the above one (that it is impossible for a hting to be and not be), they would have to understand the concepts that make up that proposition. An example will hardly be found among young children in which one would actually be able to understand what is being proposed by that proposition. They might first need to understand the idea of substance (that is, a permanence of some sort), and then in turn to understand the concept of permanence through time, and then in turn understand what a logical contradiction is. Locke argues that this, along with the fact that many grown men will hardly understand the proposition, proves innateness of speculative principles false. This does not necessarily mean the the proposition is false, but rather that an assent or denial can only come once someone has been educated.