We see, then, that error in the process of introspection is at least conceivable.  And now let us examine this process a little further, in order to find out what probabilities of error attach to it.

To begin with, then, an act of introspection, to be complete, clearly involves the apprehension of an internal feeling or idea as something mental and marked off from the region of external experience.  This distinct recognition of internal states of mind as such, in opposition to external impressions, is by no means easy, but presupposes a certain degree of intellectual culture, and a measure of the power of abstract attention.

Confusion of Internal and External Experience.

Accordingly, we find that where this is wanting there is a manifest disposition to translate internal feelings into terms of external impressions.  In this way there may arise a slight amount of habitual and approximately constant error.  Not that the process approaches to one of hallucination; but only that the internal feelings are intuited as having a cause or origin analogous to that of sense-impressions.  Thus to the uncultivated mind a sudden thought seems like an audible announcement from without.  The superstitious man talks of being led by some good or evil spirit when new ideas arise in his mind or new resolutions shape themselves.  To the simple intelligence of the boor every thought presents itself as an analogue of an audible voice, and he commonly describes his rough musings as saying this and that to himself.  And this, mode of viewing the matter is reflected even, in the language of cultivated persons.  Thus we say, “The idea struck me,” or “was borne in on me,” “I was forced to do so and so,” and so on, and in this manner we tend to assimilate internal to external mental phenomena.

Much the same thing shows itself in our customary modes of describing our internal feelings of pleasure and pain.  When a man in a state of mental depression speaks of having “a load” on his mind it is evident that he is interpreting a mental by help of an analogy to a bodily feeling.  Similarly, when we talk of the mind being torn by doubt or worn by anxiety.  It would seem as though we tended mechanically to translate mental pleasures and pains into the language of bodily sensations.

The explanation of this deeply rooted tendency to a slightly illusory view of our mental states is, I think, an easy one.  For one thing, it follows from the relation of the mental image to the sense-impression that we should tend to assimilate the former to the latter as to its nature and origin.  This would account for the common habit of regarding thoughts, which are of course accompanied by representatives of their verbal symbols, as internal voices, a habit which is probably especially characteristic of the child and the uncivilized man, as we have found it to be characteristic of the insane.