In brief, the errors of introspection, though numerous, are all too slight to render the process of introspection as a whole unsound and untrustworthy.  Though, as we have seen, it involves, strictly speaking, an ingredient of representation, this fact does not do away with the broad distinction between presentative and representative cognition.  Introspection is presentative in the sense that the reality constituting the object of cognition, the mind’s present feeling, is as directly present to the knowing mind as anything can be conceived to be.  It may be added that the power of introspection is a comparatively new acquisition of the human race, and that, as it improves, the amount of error connected with its operation may reasonably be expected to become infinitesimal.

It is often supposed by those who undervalue the introspective method in psychology that there is a special difficulty in the detection of error in introspection, owing to the fact that the object of inspection is something individual and private, and not open to common scrutiny as the object of external perception.  Yet, while allowing a certain force to this objection I would point out, first of all, that even in sense-perception, what the individual mind is immediately certain of is its own sensations.  The relatively perfect certainty which finally attaches to the presentative side of sense-perception is precisely that which finally attaches to the results of introspection.

In the second place, it may be said that the contrast between the inner and the outer experience is much less than it seems.  In many cases our emotions are the direct result of a common external cause, and even when they are not thus attached to some present external circumstance, we are able, it is admitted, by the use of language, roughly to compare our individual feelings.  And such comparison is continually bringing to light the fact that there is a continuity in our mental structure, that our highest thoughts and emotions lead us back to our common sense-impressions, and that consequently, in spite of all individual differences of temperament and mental organization, our inner experience is in all its larger features a common experience.

I may add that this supposition of the common nature of our internal experience, as a whole, not only underlies the science of psychology, but is implied in the very process of detecting and correcting errors of introspection.  I do not mean that in matters of feeling “authority” is to override “private judgment.”  Our last resort with respect to things of the mind is, as I have said, that of careful self-inspection.  And the progress of psychology and the correction of illusion proceed by means of an ever-improving exercise of the introspective faculty.  Yet such individual inspection can at least be guided by the results of others’ similar inspection, and should be so guided as soon as a general consensus in matters of internal experience is fairly made out.  In point of fact, the preceding discussion of illusions of introspection has plainly rested on the sufficiently verified assumption that the calmest and most efficient kind of introspection, in bringing to light what is permanent as compared with what is variable in the individual cognition, points in the direction of a common body of introspected fact.