Locke’s account of ideas as signs plays a fundamental role in his Essay. Given that ideas are the primary units of representing the world, the question arises what it is that determines their representation. Although the commonly held causal and teleological readings address fundamental features of how ideas represent, it remains unclear how complex ideas function as signs in our actual episodes of thought. Reconstructing the natural historical account versus the discussion of the use of ideas in thinking, I will show that Locke reflects the distinction between origin and use of idea in his Essay. Distinguishing ideas as signs of things and signs for thinkers, we can see that Locke endorses an account of signification that combines causal, ...