Some authors take high ground here and claim for it a sort of infallibility. Thus Ueberweg:
"When a mental image, as such, is the object of my apprehension, there is no meaning in seeking to distinguish its existence in my consciousness (in me) from its existence out of my consciousness (in itself); for the object apprehended is, in this case, one which does not even exist, as the objects of external perception do, in itself outside of my consciousness. It exists only within me."[189]
And Brentano:
"The phenomena inwardly apprehended are true in themselves. As they appear—of this the evidence with which they are apprehended is a warrant—so they are in reality. Who, then, can deny that in this a great superiority of Psychology over the physical sciences comes to light?"
And again:
"No one can doubt whether the psychic condition he apprehends in himself be, and be so, as he apprehends it. Whoever should doubt this would have reached that finished doubt which destroys itself in destroying every fixed point from which to make an attack upon knowledge."[190]
Others have gone to the opposite extreme, and maintained that we can have no introspective cognition of our own minds at all. A deliverance of Auguste Comte to this effect has been so often quoted as to be almost classical; and some reference to it seems therefore indispensable here.
Philosophers, says Comte,[191] have
"in these latter days imagined themselves able to distinguish, by a very singular subtlety, two sorts of observation of equal importance, one external, the other internal, the latter being solely destined for the study of intellectual phenomena.... I limit myself to pointing out the principal consideration which proves clearly that this pretended direct contemplation of the mind by itself is a pure illusion.... It is in fact evident that, by an invincible necessity, the human mind can observe directly all phenomena except its own proper states. For by whom shall the observation of these be made? It is conceivable that a man might observe himself with respect to the passions that animate him, for the anatomical organs of passion are distinct from those whose function is observation. Though we have all made such observations on ourselves, they can never have much scientific value, and the best mode of knowing the passions will always be that of observing them from without; for every strong state of passion ... is necessarily incompatible with the state of observation. But, as for observing in the same way intellectual phenomena at the time of their actual presence, that is a manifest impossibility. The thinker cannot divide himself into two, of whom one reasons whilst the other observes him reason. The organ observed and the organ observing being, in this case, identical, how could observation take place? This pretended psychological method is then radically null and void. On the one hand, they advise you to isolate yourself, as far as possible, from every external sensation, especially every intellectual work,—for if you were to busy yourself even with the simplest calculation, what would become of internal observation?—on the other hand, after having with the utmost care attained this state of intellectual slumber, you must begin to contemplate the operations going on in your mind, when nothing there takes place! Our descendants will doubtless see such pretensions some day ridiculed upon the stage. The results of so strange a procedure harmonize entirely with its principle. For all the two thousand years during which metaphysicians have thus cultivated psychology, they are not agreed about one intelligible and established proposition. 'Internal observation' gives almost as many divergent results as there are individuals who think they practise it."
Comte hardly could have known anything of the English, and nothing of the German, empirical psychology. The 'results' which he had in mind when writing were probably scholastic ones, such as principles of internal activity, the faculties, the ego, the liberum arbitrium indifferentiæ, etc. John Mill, in replying to him,[192] says: