Sense-data

The concept of sense data (singular: sense datum) is very influential and widely used in the philosophy of perception.

Many philosophers have said that the most immediate objects of perception are mental objects—objects in the mind. So within the mind there are two different items: there is a mental object, which may represent things outside the mind, and something that makes up awareness, such as the process of a perceptual act (see Husserl) or the phenomenon of an inner sense (see Immanuel Kant or Rene Descartes).

For example, according to this view, when I see the President on TV the very first thing I perceive is an image of the President in my mind. This image represents the moving picture on the television screen, and that moving picture on the television screen in turn represents the President himself.

Besides sense-data these alleged immediate mental objects of perception have been called impressions (e.g., by Hume), ideas (Berkeley), sensibilia (J. L. Austin), qualia (C. I. Lewis) and other names.

We have mental awareness of those Presidential sense-data, not with our eyes, of course, because our eyes are in the physical world, and sense-data are in the mind. Those Presidential sense-data are caused by the image of the President on the TV screen. And the sense-data represent the President to us. So generally there are supposed to be mental, internal objects of perception, which represent physical, external objects. "Internal" here just means "inside the mind" (though of course you can guess that that phrase is open to different interpretations). "External" means, correspondingly, "outside the mind" or "in the physical world."

Sense data theories have been heavily criticised by philosophers such as J.L. Austin and Wilfrid Sellars.