Some philosophers who accept that

the various forms of the argument from illusion

show that we do not directly perceive material

objects, use the terms sense-datum and sense-data

for what we do directly perceive. Unlike the

terms idea or sensation, the term sense-data does

not imply that the direct objects of perception

are mental, but leaves that question open.

Sense-data are objects of some sort, distinguished

from the act of being aware of them.

Sense-data are usually supposed to have all of

the properties they seem to have. Suppose, for

example, you see a blue tie in a store with fluorescent

lighting, it looks green, and you take it

to be so. A philosopher who believes in sensedata

would say that you are directly aware of a

sense-datum that is green; your mistake is in

your inference from the fact about the sensedatum’s

color to the tie’s color.