For John Locke, we are not primarily beings who know. We are beings who sense and learn. Locke is an empiricist, which is someone who believes that the contents of our minds are there because the world gives those contents to us. We were not born with knowledge, nor do we deduce knowledge from axioms. We pull ourselves up by our bootstraps.
So, we are collectors, organizers, comparers, and combiners of basic sensations from the world. But where, exactly, do these ideas come from, and how to they make us who we are?
The ideas come in two forms: simple and complex.
The simple ideas come from 4 places:
1. By one sense alone. This is like the sensation of colour, sound, many others. Heat and cold are particular to the sense of touch, as is the idea of solidity.
2. By more than one sense. We get ideas like those of space, figure, rest and motion from more than one sense. It's usually touch + some other sense, although we can see, hear, and touch motion.
3. By reflection alone. This is the operation of the mind as it considers the ideas produced by sense. The idea of perception and of willing are from reflection.
4. By sensation and reflection. Most of our ideas are here.
So what do we perceive, when we perceive ideas? Primary and Secondary (and maybe also Tertiary) Qualities of things:
Besides simple ideas, we also have complex ideas (Bk. II, ch. 12). Our minds, using their various faculties, put together ideas (either simple combination, or comparing two ideas) and take them apart (abstraction to produce general ideas). There are three categories of complex ideas:
Modes: These are ideas that are parts of, or dependent on substances. Beauty, for instance, is an idea which is constructed from simple ideas of form, colour, figure, and other things.
Substances: We do not perceive substances, we only perceive various qualities. A substance is part of a complex idea we have, which gives something particularity.
Relations: A complex idea that is the relation of other ideas.
Example: The idea of power is a simple idea, which we get from the combination of certain sensations with ideas of change. Power is not perceived as power; rather, the mind takes note of changes in sensation. This looks a lot like a complex idea, but Locke insists that it is a simple idea. There is both passive and active power. Passive power: things have the power to change in some way. It means that they have the power of being acted upon. The best example of active power is our power of will. Notions like desire and freedom as well as will get outlined in terms of power.
For Locke, there is a war between the passions and rationality. This is part of who we are. Our minds want to work with the assembled ideas we have, while our "bodies" want to have immediate gratification. Our passions are our wants, and being a person (or at least, a civilized person) means to have control over the passions.