Rightly considered, bodies have three sorts of qualities: (1) primary qualities—bulk, figure, number, situation, and motion or rest of solid parts—which are in things regardless of perception and give us an idea of the thing as it is in itself; (2) powers, grounded in their insensible primary qualities, to operate on our senses and produce ideas of colours, sounds, tastes, etc., usually called sensible qualities; and (3) powers, also grounded in their primary constitution, to change the primary qualities of other bodies so as to alter how those bodies operate on our senses.

By John Locke, from An Essay Concerning Human Understanding

Key Arguments

  • Locke begins, 'The qualities, then, that are in bodies, rightly considered, are of three sorts:—'
  • First, he lists what he calls primary: 'First, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things. These I call primary qualities.'
  • Secondly, he introduces what are 'usually called sensible qualities': 'Secondly, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in us the different ideas of several colours, sounds, smells, tastes, &c. These are usually called sensible qualities.'
  • Thirdly, he describes another sort of power: 'Thirdly, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of another body, as to make it operate on our senses differently from what it did before. Thus the sun has a power to make wax white, and fire to make lead fluid. These are usually called powers.'
  • He then restates their status: 'The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend. The other two are only powers to act differently upon other things: which powers result from the different modifications of those primary qualities.'

Source Quotes

Three sorts of qualities in bodies. The qualities, then, that are in bodies, rightly considered, are of three sorts:— First, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things.
Three sorts of qualities in bodies. The qualities, then, that are in bodies, rightly considered, are of three sorts:— First, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things. These I call primary qualities. Secondly, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in us the different ideas of several colours, sounds, smells, tastes, &c.
These I call primary qualities. Secondly, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in us the different ideas of several colours, sounds, smells, tastes, &c. These are usually called sensible qualities. Thirdly, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of another body, as to make it operate on our senses differently from what it did before.
These are usually called sensible qualities. Thirdly, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of another body, as to make it operate on our senses differently from what it did before. Thus the sun has a power to make wax white, and fire to make lead fluid. These are usually called powers. The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend.
These are usually called powers. The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend. The other two are only powers to act differently upon other things: which powers result from the different modifications of those primary qualities. 24.

Key Concepts

  • The qualities, then, that are in bodies, rightly considered, are of three sorts:—
  • First, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things. These I call primary qualities.
  • Secondly, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in us the different ideas of several colours, sounds, smells, tastes, &c. These are usually called sensible qualities.
  • Thirdly, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of another body, as to make it operate on our senses differently from what it did before. Thus the sun has a power to make wax white, and fire to make lead fluid. These are usually called powers.
  • The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend. The other two are only powers to act differently upon other things: which powers result from the different modifications of those primary qualities.

Context

Book II, chapter VIII, section 23, where Locke lays out his threefold classification of bodily qualities into primary qualities, sensible qualities (secondary), and further powers (tertiary) to change other bodies.