All ideas in the human understanding originate from experience, which has only two fountains: sensat… — John Locke

All ideas in the human understanding originate from experience, which has only two fountains: sensation of external objects and reflection on the mind’s own operations; the mind at first is like 'white paper, void of all characters.'

By John Locke, from An Essay Concerning Human Understanding

Key Arguments

Locke asks us to 'suppose the mind to be, as we say, white paper, void of all characters, without any ideas' and then asks how it comes to be furnished.
He answers that the mind gets 'all the materials of reason and knowledge' 'in one word, from EXPERIENCE', on which 'all our knowledge is founded'.
Experience splits into observation of 'external sensible objects' and of 'the internal operations of our minds perceived and reflected on by ourselves', which 'supplies our understandings with all the materials of thinking'.
These two sources are 'the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring', denying any third (innate) origin.

Source Quotes

All ideas come from sensation or reflection. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas:— How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety?

Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded; and from that it ultimately derives itself.

To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking.

In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.

Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring. 3.

Key Concepts

Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas:— How comes it to be furnished?
Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE.
In that all our knowledge is founded; and from that it ultimately derives itself.
Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking.
These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.

Context

Book II, chapter I, section 2, where Locke introduces his empiricist 'tabula rasa' doctrine and the two basic sources of all ideas.