In most cases of these alleged philosophical errors, however, the active and passive factors seem to combine.  There are certain intricacies in the mental phenomenon itself favouring the chances of error, and there are independent predispositions leading the mind to look at the phenomenon in a wrong way.  This seems to apply to the famous declaration of a certain school of thinkers that by an act of introspection we can intuit the fact of liberty, that is to say, a power of spontaneous determination of action superior to and regulative of the influence of motives.  It may be plausibly contended that this idea arises partly from a mixing up of facts of present consciousness with inferences from them, and partly from a natural predisposition of the mind to invest itself with this supreme power of absolute origination.[106]

In a similar way, it might be contended that other famous philosophic dicta are founded on a process of erroneous introspection of subjective mental states.  In some cases, indeed, it seems a plausible explanation to regard these illusions as mere survivals in attenuated shadowy form of grosser popular illusions.  But this is not yet the time to enter on these, which, moreover, hardly fall perhaps under our definition of an illusion of introspection.

Value of the Introspective Method.

In drawing up this rough sketch of the illusions of introspection, I have had no practical object in view.  I have tried to look at the facts as they are apart from any conclusions to be drawn from them.  The question how far the liability to error in any region of inquiry vitiates the whole process is a difficult one; and the question whether the illusions to which we are subject in introspection materially affect the value of self-knowledge as a whole and consequently of the introspective method in psychology, as many affirm, is too subtle a one to be fully treated now.  All that I shall attempt here is to show that it does not do this any more than the risk of sense-illusion can be said materially to affect the value of external observation.

It is to be noted first of all that the errors of introspection are much more limited than those of sense-perception.  They broadly answer to the slight errors connected with the discrimination and recognition of the sense-impression.  There is nothing answering to a complete hallucination in the sphere of the inner mental life.  It follows, too, from what has been said above, that the amount of active error in introspection is insignificant, since the representation of a feeling or belief is so very similar to the actual experience of it.