3. Ibn al-Haitham’s thinking is expressed in quite a mathematical style. The Substance of a body consists, according to him, of the sum of its essential attributes, just as a whole is equal to the sum of its parts, and a concept to the sum of its marks. [[151]]
In the “Optics” the psychological remarks on Seeing and on Sense-Perception in general—are of special interest for us. Here he exerts himself to separate the individual Moments of the Perception, and to give prominence to the condition of Time as characterizing the whole process.
Perception then is a compound process, arising out of (1) sensation, (2) comparison of several sensations or of the present sensation with the memory-image which has been gradually formed in the soul as a result of earlier sensations, and (3) recognition, in such fashion that we recognize the present percept as equivalent to the memory-image. Comparison and recognition are not activities of the Senses, which merely receive impressions passively, but they devolve upon the Understanding as the faculty of judgment. Ordinarily the whole process goes forward unconsciously or semi-consciously, and it is only through reflection that it is brought within our consciousness, and that the apparently simplex is separated into its component parts.
The process of Perception is gone through very quickly. The more practice a man has in this respect, and the oftener a perception is repeated, the more firmly is the memory-image stamped upon the soul, and the more rapidly is recognition or perception effected. The cause of this is that the new sensation is supplemented by the image which is already present in the soul. One might thus be disposed to think that Perception was an instantaneous act, at least after long practice. That, however, would be erroneous, for not only is every sensation attended by a corresponding change localized in the sense-organ, which demands a certain time, but also, between the stimulation of the organ and the consciousness of the perception [[152]]an interval of time must elapse, corresponding to the transmission of the stimulus for some distance along the nerves. That it needs time, for example, to perceive a colour, is proved by the rotating circle of colours, which shows us merely a mixed colour, because on account of the rapid movement we have no time to perceive the individual colours.
Comparison and Recognition are, according to Ibn al-Haitham, the significant Mental Moments of Perception. On the other hand Sensation tallies with the Material; and the Sense experiencing the sensation exhibits a passive attitude. Properly all sensation is in itself a kind of discomfort, which ordinarily does not make itself felt, but which emerges into consciousness under very strong stimuli, for example, through too bright a light. A pleasurable character accrues only to the completed perception, that is to the recognition which lifts the material given in sensation, up to the mental form.
The comparison and recognition, which are put in operation in Perception, constitute an unconscious judgment and conclusion. The child is already drawing a conclusion, when of two apples he chooses the finer one. As often as we comprehend a connection, we are concluding. But, since judging and concluding are quickly settled, men are easily misled in this matter, and frequently they regard as an original concept that which is merely a judgment derived by a process of ratiocination. In the case of everything which is announced to us as an axiom, we should be on our guard and trace it up, to see whether it cannot be derived from something more simple.
4. This appeal of our philosopher had little effect in the [[153]]East. It is true that in Mathematics and Astronomy he created somewhat of a school; but his Aristotelian philosophy had comparatively few admirers. We know only one of his scholars who is counted among the Philosophers, Abu-l-Wafa Mubasshir ibn Fatik al-Qaid, an Egyptian emir, who in the year 1053 produced a work made up of proverbial wisdom, anecdotes in illustration of the history of philosophy, and so on. Hardly anything can be traced in it which is the result of his own thinking. It should have been pleasant reading. And the inhabitants of Cairo in after times found edification,—more even than in such a work,—in the tales of the Thousand and One Nights.
The East set the stigma of heresy upon Ibn al-Haitham and his works, and now it has almost completely forgotten him. A disciple of Maimonides, the Jewish philosopher, relates that he was in Bagdad on business, when the library of a certain philosopher, (who died in 1214) was burned there. The preacher, who conducted the execution of the sentence, threw into the flames, with his own hands, an astronomical work of Ibn al-Haitham, after he had pointed to a delineation therein given of the sphere of the earth, as an unhappy symbol of impious Atheism. [[154]]
[1] Cf. my Article “On Kindi and his School” in Stein’s ‘Archiv für Geschichte der Philosophie XIII’, p. 153 sqq., from which I have taken over, without much alteration, not a little that appears in this chapter. [↑]