The accurate recognition of an impression of colour depends, as we have seen, on this process of classing being correctly performed.

Similarly, the recognition of internal feelings implies the presence of the appropriate or corresponding class-representation.

Accordingly, if it is possible for a wrong representation to get substituted for the right one, there seems to be an opening for error.
Any error that would thus arise can, of course, only be determined as such in relation to some other act of introspection of the same mind.

In matters of internal perception other minds cannot directly assist us in correcting error as they can in the case of external perception, though, as we shall see by-and-by, they may do so indirectly.

The standard of reality directly applicable to introspective cognition is plainly what the individual mind recognizes at its best moments, when the processes of attention and classifying are accurately performed, and the representation may be regarded with certainty as answering to the feeling.