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• Introductory Note.
• Book I.
• Chap. I.: Whether a Demonstrative Science Exists
• Chap. II.: What Knowing Is, What Demonstration Is, and of What It Consists
• Chap. III.: A Refutation of the Error Into Which Some Have Fallen Concerning Science and Demonstration
• Chap. IV.: The Meaning of ‘distributive,’ ‘essential,’ ‘universal’
• Chap. V.: From What Causes Mistakes Arise With Regard to the Discovery of the Universal. How They May Be Avoided
• Chap. VI.: Demonstration Is Founded On Necessary and Essential Principles
• Chap. VII.: The Premises and the Conclusion of a Demonstration Must Belong to the Same Genus
• Chap. VIII.: Demonstration Is Concerned Only With What Is Eternal
• Chap. IX.: Demonstration Is Founded Not On General, But On Special and Indemonstrable Principles; Nor Is It Easy to Know Whether One Really Possesses Knowledge Drawn From These Principles
• Chap. X.: The Definition and Division of Principles
• Chap. XI.: On Certain Principles Which Are Common to All Sciences
• Chap. XII.: On Questions, And, In Passing, On the Way In Which Sciences Are Extended
• Chap. XIII.: The Difference Between the Demonstration and Science of a Thing’s Nature and Those of Its Cause
• Chap. XIV.: The Figure Proper to Demonstrate Syllogism
• Chap. XV.: On Immediate Negative Propositions
• Chap. XVI.: On Ignorance Resulting From a Defective Arrangement of Terms In Mediate Propositions
• Chap. XVII.: On Ignorance Resulting From a Defective Arrangement of Terms In Immediate Propositions
• Chap. XVIII.: On Ignorance As Resulting From Defective Sense Perception
• Chap. XIX.: Whether the Principles of Demonstration Are Finite Or Infinite
• Chap. XX.: Middle Terms Are Not Infinite
• Chap. XXI.: In Negations Some Final and Ultimate Point Is Reached Where the Series Must Cease
• Chap. XXII.: In Affirmations Some Final and Ultimate Point Is Reached Where the Series Must Cease
• Chap. XXIII.: Certain Corollaries
• Chap. XXIV.: Whether Universal Or Particular Demonstration Is Superior
• Chap. XXV.: That Affirmative Is Superior to Negative Demonstration
• Chap. XXVI.: Direct Demonstration Is Superior to Reduction Per Impossible
• Chap. XXVII.: What Science Is More Certain and Prior, and What Less Certain and Inferior
• Chap. XXVIII.: What Constitutes One Or Many Sciences
• Chap. XXIX.: Concerning Many Demonstrations of the Same Thing
• Chap. XXX.: On Fortuitous Occurrences
• Chap. XXXI.: Sense Perception Cannot Give Demonstrative Science
• Chap. XXXII.: On the Difference of Principles Corresponding to the Difference of Syllogisms
• Chap. XXXIII.: The Distinction Between Science and Opinion
• Chap. XXXIV.: On Sagacity
• Book II.
• Chap. I.: On the Number and Arrangements of Questions
• Chap. II.: Every Question Is Concerned With the Discovery of a Middle Term
• Chap. III.: The Distinction Between Definition and Demonstration
• Chap. IV.: The Essence of a Thing Cannot Be Attained By Syllogism
• Chap. V.: Knowledge of the Essence Cannot Be Attained By Division
• Chap. VI.: The Essence Cannot Be Proved By the Definition of the Thing Itself Or By That of Its Opposite
• Chap. VII.: Whether the Essence Can In Any Way Be Proved
• Chap. VIII.: How the Essence Can Be Proved
• Chap. IX.: What Essences Can and What Cannot Be Proved
• Chap. X.: The Nature and Forms of Definition
• Chap. XI.: The Kinds of Causes Used In Demonstration
• Chap. XII.: On the Causes of Events Which Exist, Are In Process, Have Happened, Or Will Happen
• Chap. XIII.: On the Search For a Definition
• Chap. XIV.: On the Discovery of Questions For Demonstration
• Chap. XV.: How Far the Same Middle Term Is Employed For Demonstrating Different Questions
• Chap. XVI.: On Inferring the Cause From the Effect
• Chap. XVII.: Whether There Can Be Several Causes of the Same Thing
• Chap. XVIII.: Which Is the Prior Cause, That Which Is Nearer the Particular, Or the More Universal?
• Chap. XIX.: On the Attainment of Primary Principles
• Appendix. Prior Analytics. Book II.
• Chap. XXIII.: On Induction
• XXIV.: On Example

CHAP. XXXI.

Sense perception cannot give Demonstrative Science

Nor can scientific knowledge be gained by means of sense perception, for even though perception may give information concerning a thing’s quality as opposed to its concrete existence, yet an act of perception must indicate the existence of the object in a particular place and at the present time. The universal on the other hand and that which is present in every example of a subject cannot be perceived by the senses, for the universal is not a particular thing visible at the present moment, for then it would not be a universal at all, seeing that we mean by Universal that which is eternal and omnipresent. Since the demonstrations rest on the universal, and universals cannot be perceived by the senses, it is clear that one cannot acquire scientific knowledge by means of sense perception. Even if we could have perceived that a triangle has its angles equal to two right angles, we should certainly have gone on to search for a demonstration of it, and should not, as some assert, have already known the fact by means of perception alone. Perception as an act must deal with the particular alone, while scientific knowledge consists in learning the universal. Thus even if we were on the moon and saw the earth shutting out the light, we should nevertheless be ignorant of the cause of an eclipse. We should indeed see that the moon was being eclipsed at that particular moment, but we should not know the cause of an eclipse in general, for our perception would not be of the universal. I do not deny that after seeing the same phenomenon occur repeatedly we might search out the universal law, and thus attain to demonstration, seeing that knowledge of the universal results from repeated acts of sense perception. But the value of the universal lies in its shewing the cause of particular phenomena, and consequently the universal is more important than the perception of particular cases or the immediate apprehension of such things as have for cause something other than themselves. Of self-caused primaries we are not now speaking. It is then clearly impossible to acquire scientific knowledge of any demonstrable thing, unless the meaning of ‘scientific knowledge acquired through demonstration’ be attached to the phrase ‘act of sense-perception.’

Certain doubtful questions may be solved by a reference to the failure of the sense perceptions. Thus if we had seen certain things we should have made no further enquiry about them, not because we know them simply from seeing them, but because the mere sight of them would have sufficed to give us the universal. E.g. If we saw that the burning-glass was porous and that the light filtered through the apertures, it would be clear why it burns, because we should see the phenomenon occur in every separate glass; but we should yet have to form the abstract idea that this quality is universally true of every possible glass1 .

[1 ]This translation follows the reading διὰ τί καίει with the Clarendon Press Edition. Poste, Zell and other versions follow the old reading ϕωτίζει ‘transmits light,’ and make ὔελσς refer to all kinds of glass.