LESSON 2

Unity as a Measure

  Chapter 1: 1052b 19-1053b 8

             820. But the essence of oneness or unity consists especially in being the first measure of each genus, and most properly of quantity; because it is from this genus that it is transferred to the others. For a measure is that by which quantity is first known; and quantity as quantity is known either by unity or by a number, and every number is known by unity. Hence all quantity as quantity is known by unity.

             821. And that by which quantity is first known is unity itself; and for this reason unity is the principle of number as number.

             822. And the measure of other things is also that by which each is first known. And the measure of each is a unit: in length, in breadth, in depth, and in heaviness and in rapidity. For the terms heavy and rapid are common to both contraries, since each of them has two meanings. Thus heavy is said both of what has any amount of inclination towards the center and of what has an excessive inclination; and rapid is said both of what has any amount of motion, and of what has an excessive motion. For even what is slow has a certain speed, and what is light a certain heaviness.

             823. And in all these cases the measure and principle is something one and indivisible, since even in the case of lines we use the foot measure as something indivisible. For everywhere men seek as a measure something one and indivisible, and this is what is simple either in quality or in quantity. Hence wherever it seems impossible to add or to subtract anything, there the most certain measure is found. The measure of number, then, is the most certain; for men claim that the unit is indivisible in every respect. And in other cases they imitate such a measure; for any addition or subtraction might more easily escape our notice in the case of a furlong or of a talent or of anything which is always a larger measure than in that of something which is a smaller measure. Hence it is the first thing from which no perceptible subtraction can be made that all men make a measure, whether of liquids or of solids or of weight or of size; and they think they know the quantity of a thing when they know it by this measure.

             824. And they also measure motion by that motion which is simple and most rapid; for this takes the least time. Hence in astronomy this kind of unit is the principle and measure; for astronomers suppose the motion of the heavens to be uniform and most rapid, and they judge the other motions by this motion. And in music the diesis is the measure, because it is the smallest interval; and in speech, the letter. And all of these are one, not in the sense that there is something common to all which is one, but in the sense that we have explained.

             825. However, a measure is not always numerically one, but sometimes many; for example, there are two dieses not discernible by ear but differing in their ratios. And the words by which we measure speech are many; and the diagonal of a square is measured by two quantities, and so also is a side; and so are all continuous quantities. Therefore all things have as their measure some unit, because we come to know the things of which substance is composed by dividing it either in regard to quantity or to species. Hence the unit is indivisible, because what is first in each class of things is indivisible. But not every unit is indivisible in the same way, for example, the foot and the unit; but the latter is indivisible in every respect, whereas the former belongs to that class of things which are indivisible from the viewpoint of the senses, as has already been stated (823); for perhaps every continuous thing is divisible.

             826. And a measure is always of the same kind as the thing measured; for the measure of continuous quantities is a continuous quantity; and in particular the measure of length is a length; and of breath a breadth; and of width a width; and of vocal sounds a vocal sound; and of weight a weight; and of units a unit. For this is the view which must be taken, but not that the measure of numbers is a number. We should indeed have to speak in this way if we were to use parallel forms, but the meaning does not require such parallels: it would be as if the measure of units had to be designated as units and not as a unit. But number is a plurality of units.

             827. And for the same reason we say that knowledge and perception are the measure of things, because we know something by them; yet they are measured rather than measure. But in our own case it is as though someone else were measuring us, and we learned how big we are by means of the cubit measure being applied to so much of us. But Protagoras says that man is the measure of all things, as if he were saying the man who knows or the man who perceives; and these because the one has intellectual knowledge and the other sensory perception, which we say are the measures of the things that are placed before them. Hence, while these men say nothing extraordinary, they seem to be saying something important.

             828. It is evident, then, that unity in the strictest sense, according to the definition of the term, is a measure, and particularly of quantity and then of quality. And some things will be such if they are indivisible in quantity, and others if they are indivisible in quality. Therefore what is one is indivisible either in an unqualified sense or inasmuch as it is one.

COMMENTARY

             1937. Having explained the various senses in which unity is predicated of things, and having stated what its essential note is, to which all its usages are reduced, i.e., being indivisible, here the Philosopher infers a property of unity from its essential note, namely, that it is a measure. This is divided into two parts. In the first (820:C 1937) he shows how the notion of a measure belongs to unity and to the various classes of accidents. In the second (829:C 1961) he shows how unity in the sense of a measure is found in substances ("It is necessary").

             In regard to the first part of this division he does two things. First, he indicates the class of things in which unity in the sense of a measure is primarily found, and how it is transferred from this class to the others with the proper notion of a measure. Second (827:C 1956), he explains how it is transferred figuratively to the other classes ("And for the same reason").

             In treating the first part he does two things. First, he indicates the class of things in which unity in the sense of a measure is first found, and how it is transferred from this class to the others. Second (825:C 1950), he makes a study of measures ("However, a measure").

             In regard to the first he does three things. First, he shows how unity as a measure is found in quantity, and how it is transferred from this category to the others. Second (821:C 1939), he indicates the species of quantity in which it is first found ("And that by which"). Third (822:C 1940), he shows how it is transferred to other species of quantity ("And the measure").

             1938. He accordingly says, first (820), that, since the essential note of unity consists in being indivisible, and what is indivisible in each genus is somehow the measure of that genus, unity must be said to be in the highest degree the first measure of each genus. This is said to apply most properly to quantity, and it is from this class that the notion of a measure is transferred to other classes of things. Now a measure is nothing else than that by which a thing's quantity is known, and this is known by the unit or by a number: by a unit, as when we say one furlong or one foot; and by a number, as when we say three furlongs or three feet. Again, every number is known by the unit, because the unit taken a certain number of times gives a number. It follows, then, that every quantity is known by unity. To "quantity" he adds "as quantity," intending that this be referred to the measure of quantity; for the properties and other accidents of quantity are known in a different way.

             1939. And that by which (821).

             Then he indicates in what species of quantity unity or measure is primarily found. First, he makes it clear that the notion of a measure is primarily found in discrete quantity, which is number. He says that that by which quantity is first known is "unity itself," i.e., the unit which is the principle of number. For in other species of quantity the unit is not unity itself but something of which unity is an attribute, as when we speak of one hand or of one continuous quantity. Hence it follows that unity itself, which is the first measure, is the principle of number as number.

             1940. And the measure (822).

             Second, he shows how unity is transferred to other species of quantity; and in regard to this he does two things. First, he indicates the species of quantity to which it is transferred. He says that it is from this class, i.e., from number and from the unit, which is the principle of number, that the notion of a measure is transferred to other quantities as that by which each of them is first known. And whatever is the measure in each class of things is the unit in that class.

             1941. He gives examples of this in three classes of things, i.e., in dimensions--length, breadth and width; in weight, or in what he calls heaviness; and in speed, or in what he calls rapidity, which refers to the measure of time. In the case of dimensions no one doubted that they were quantities and that they were properly susceptible to measurement, but in the case of weight and of speed there could be a difficulty because these seem to be qualities rather than quantities.

             1942. He therefore explains how these pertain to the genus of quantity, and how they are susceptible to measurement. He says that heaviness and rapidity have something in common with their contraries because one contrary is found in the other; for what is heavy is in some sense light, and the reverse; and what is rapid is in some sense slow. For each of these terms is used in two senses. In one sense the term heavy is used without qualification of anything that has an inclination to be borne towards the center of the earth, without taking into consideration how great its inclination is; and in this sense heavy does not refer to the category of quantity, and it is not susceptible to measurement. In the other sense it is used of one thing in comparison with something else, namely, of what exceeds something else in terms of the above-mentioned inclination; for example, we say that earth is heavy in comparison with water, and that lead is heavy in comparison with wood. Therefore it is by reason of this excess that some notion of quantity and measure is found. The term rapid is similarly used in two senses. In one sense it is used without qualification of anything that has any motion; and in a second sense it is used of anything that has an excessive motion. And in one respect the notions of quantity and measure properly apply to it, and in another respect they do not.

             1943. With a view to clarifying his statement about the condition of heaviness and rapidity in reference to contraries he adds that rapidity is found in something that is slow inasmuch as what is simply and unqualifiedly slow is more rapid in comparison with something that is slower than itself. And in a similar way heaviness is found in light things; for example, air is light in comparison with earth, and heavy in comparison with fire.

             1944. And in all cases (823).

             Then he shows how the notion of a measure is transferred from number to other kinds of quantity. He immediately makes this clear, first, in the case of dimensions and in that of weights; and second (824:C 1947), in that of the rapidity of motions ("And they also measure").

             He accordingly says, first (823), that the notion of a measure is transferred from number to the other kinds of quantity in this way that, just as the unit which is the measure of number is indivisible, so too all the other kinds of quantity have something that is one and indivisible as their measure and principle. For example, in measuring lines men use "the foot measure," i.e., the measure of one foot, as something indivisible; for wherever something indivisible is sought as a measure, there is something simple either in quality or in quantity; in quality, as whiteness in the case of colors, which is in a sense the measure of colors, as will be mentioned below (831:C 1968); and in quantity, as the unit in the case of numbers, and the foot measure in the case of lines.

             1945. Further, he points out why a measure must be something indivisible. The reason is that an exact measure must be something which can be neither added to nor subtracted from. Thus the unit is the most exact or certain measure, because the unit which is the principle of number is altogether indivisible, and whatever unity is not susceptible either to addition or to subtraction remains one. The measures of the other classes of quantity resemble this unit which is indivisible inasmuch as men take some smallest thing as a measure to the extent that this is possible. For if anything large were taken, as the furlong among distances and the talent among weights, it would escape our notice if some small portion were subtracted from or added to it. And this would always be more true of a larger measure than of a smaller one.

             1946. Hence all men take this as a measure both in the case of liquids, such as oil and wine, and in that of solids, such as grain and barley; and also in that of weights and dimensions, which are designated as heaviness and continuous quantity. And this is first found to be such that nothing perceptible can be subtracted from it or added to it that might escape our notice. And men think they know the quantity of a thing exactly when they know it by the smallest measure of this kind.

             1947. And they also (824).

             Then he makes the same thing clear with regard to the rapidity of motions. He says that men also measure motion "by that motion which is simple," i.e., the motion which is uniform and quickest, because it takes the least time. Hence in astronomy they take such motion as the basis of measurement; for they take the motion of "the first heaven," i.e., the daily motion, which is regular and quickest, and they judge and measure all other motions by this.

             1948. And because the low and high pitch of sounds results from the quickness and slowness of motions, as is established in the science of music, he adds as an example the measurement of sounds. He says that in music the first measure is the "diesis," i.e., the difference between two half tones; for a tone is divided into two unequal half tones, as is proved in the science of music. And similarly in speech the measure is the letter, because the shortness or length of a word is a natural consequence of the quickness or slowness of a motion.

             1949. Now all these measures are something one, not in the sense that some measure is common to all, but in the sense that any measure in itself is something one, as has been pointed out.

             1950. However, a measure (825).

             After having shown in what class of things unity as a measure is primarily found, here the Philosopher clears up certain points that have to be investigated about measures.

             The first of these is that, although a measure is understood to be one thing inasmuch as it comes close to being indivisible, it is not necessary that a measure be something numerically one; but sometimes many things are measures; for example, in the case of musical sounds "there are two dieses," i.e., two half tones. However, because of their smallness they are not distinguished by the sense of hearing, for the senses do not perceive the difference between two things that are very small; but their difference is perceived "in their ratios," i.e., in the different ratios which comprise their proportions, because they are caused by different numerical proportions.

             1951. Similarly the things by which we measure words are also many; for the quantity of one meter or of one foot is measured by different syllables, some of which are short and some long. The same thing is true of the diameter of a circle and of the diagonal of a square, and also of the side of a square. And any continuous quantity is measured by two things, for an unknown quantity is found only by means of two known quantities.

             1952. Having said this he brings this part of his discussion to a close by summarizing what has been said above, namely, that unity constitutes the measure of all things. The reason for this is that unity is the term of division. And those principles which constitute the substance of each thing are known by the division or dissolution of the whole into its component parts, whether they are quantitative parts or specific parts such as matter and form and the elements of compounds. Therefore what is one in itself must be indivisible since it is the measure by which a thing is known, because in the case of singular things whatever is first in the process of composition and last in the process of dissolution is indivisible, and it is by means of this that the thing is known, as has been explained.

             1953. Yet indivisibility is not found in all things in the same way. Some things are altogether indivisible, such as the unit which is the basis of number, whereas others are not altogether indivisible but only to the senses, according as the authority of those who instituted such a measure wished to consider something as a measure; for example, the foot measure, which is indivisible in proportion [to the things measured] but not by nature. "For perhaps everything continuous is divisible"; and he says "perhaps" because of the difficulty facing those men who claimed that continuous quantity is composed of indivisible elements, or that natural continuous quantities are not infinitely divisible, but only mathematical quantities. For it is possible to find the smallest amount of flesh, as is mentioned in Book I of the Physics.

             1954. And a measure (826).

             Then he gives the second point that has to be investigated about a measure. He says that "the meter," i.e., the measure, should always be of the same kind as the thing measured, i.e., of the same nature or measure as the thing measured; for example, a continuous quantity should be the measure of continuous quantities; and it is not enough that they have a common nature, as all continuous quantities do, but there must be some agreement between the measure and the thing measured in the line of their special nature. Thus a length is the measure of lengths, a width of widths, a vocal sound of vocal sounds, a weight of weights, and a unit of units.

             1955. "For this is the view which must be taken" in order that we may speak without being criticized, "but not that number is the measure of numbers." Now number does not have the notion of a first measure but unity does; and if unity is a measure, then in order to signify the agreement between the measure and the thing measured it will be necessary to say that unity is the measure of units and not of numbers. Yet if the truth of the matter be taken into consideration, it will be necessary to admit also that number is the measure of numbers or even that the unit may be taken in a similar way as the measure of numbers. But it does not seem equally fitting to say that the unit is the measure of units and number of number or unity of number, because of the difference which appears to exist between the unit and number. But to observe this difference is the same as if someone were to say that it is fitting for units to be the measure of units but not the unit, because the unit differs from units as things expressed in the singular differ from those expressed in the plural. And the same argument applies to number in relation to the unit, because a number is nothing else than a plurality of units. Hence to say that the unit is the measure of number is merely to say that the unit is the measure of units.

             1956. And for the same reason (827).

             Then he shows how the term measure is transferred in a figurative way to another class of things. He says that, since it has been stated that a measure is that by which the quantity of a thing is known, we may say that intellectual knowledge is the measure of that which is knowable intellectually, and that sensory perception is the measure of that which is perceptible; because we know something by means of them, namely, sensible objects by means of perception and intelligible objects by means of intellectual knowledge; but we do not know them in the same way that we know something by means of a measure. For something is known by a measure as by a principle of knowledge; but things are known by sensory perception and by intellectual knowledge as by a cognitive power or cognitive habit.

             1957. Therefore they are called measures figuratively, because in reality they are measured rather than measure. For it is not because we perceive or know a thing that it is so in reality; but it is because it is so in reality that we have a true knowledge or perception of it, as is said in Book IX (807:C 1896). Thus it follows that in perceiving and knowing something we measure our knowledge by means of the things which exist outside the mind.

             1958. However, in knowing and measuring ourselves by some other measure we know how much bodily quantity we have by applying the cubit measure to ourselves. Hence, just as the external cubit is offered as a measure of our bodily quantity, in a similar way the things known or sensuously apprehended are the measures whereby we can know whether we truly apprehend something by our senses or by our intellect.

             1959. And if there is a science which is the cause of the thing known, it must be this science which measures that thing, just as the science of the master planner is the measure of things made by art, because anything made by art is complete insofar as it attains a likeness to the art. It is in this way that the science of God is related to all things. But Protagoras said that man is the measure of all things inasmuch as he knows or perceives them, because knowledge and perception are the measure of substances, i.e., of things which are intelligible and perceptible. For the followers of Protagoras, as has been stated in Book IV (344:C 637), said that things are such because we so perceive them or judge about them. Therefore, although they say nothing extraordinary or important, they nevertheless seem to be saying something of consequence, because they covertly insinuate their doctrine.

             1960. It is evident (828).

             Then he sums up the points discussed, namely, that the notion of unity involves being a measure; and this applies most properly to quantity, and then to quality and to the other genera, because anything that is a measure should be indivisible either in quantity or in quality. Thus it follows that unity is indivisible, "either in an unqualified sense" as the unit which is the basis of number, or "in a qualified sense," i.e., to the extent that it is one, as was stated with regard to the other measures.