Sensation is the first great source of ideas: the senses, as they are affected by external objects, … — John Locke

Sensation is the first great source of ideas: the senses, as they are affected by external objects, convey into the mind perceptions of sensible qualities such as colors, temperatures, tastes, and textures.

By John Locke, from An Essay Concerning Human Understanding

Key Arguments

Our senses, 'conversant about particular sensible objects', convey into the mind 'several distinct perceptions of things, according to those various ways wherein those objects do affect them'.
In this way we get ideas of 'yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities'.
Locke carefully clarifies that when he says the senses 'convey into the mind', he means that external objects convey 'what produces there those perceptions', keeping within his representational account.
Because this source depends wholly on the senses and is derived by them to the understanding, Locke names it 'SENSATION'.

Source Quotes

The objects of sensation one source of ideas. First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them. And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions.

First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them. And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions. This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call SENSATION.

And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions. This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call SENSATION. 4.

Key Concepts

First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them.
And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities;
which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions.
This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call SENSATION.

Context

Book II, chapter I, section 3, where Locke defines and illustrates 'sensation' as one of the two original sources of ideas.