Archive for the ‘Shormann Math’ category

Letters of Euler to a German Princess, Vol. II, Letter XI

July 5, 2018

This is the fifth of eleven Letters of Euler I will rewrite and post on the subject of infinitesimals (the infinitely small), an idea that is fundamental to a good understanding of calculus. Click here to read the previous letter.

Letter XI. Reflections on Divisibility in infinitum, and on Monads.

In speaking of the divisibility of body, we must carefully distinguish what is in our power, from what is possible in itself. In the first sense, it cannot be denied, that such a division of a body as we are capable of, must be very limited.

By pounding a stone we can easily reduce it to powder; and if it were possible to reckon all the little grains which form that powder, their number would undoubtedly be so great, that it would be matter of surprize, to have divided the stone into so many parts. But these very grains will be almost indivisible with respect to us, as no instrument we could employ would be able to lay hold of them. But it cannot with truth be affirmed that they are indivisible in themselves. You have only to view them with a good microscope, and each will appear itself a considerable stone, on which are distinguishable a great many points and inequalities; which demonstrates the possibility of a farther division, though we are not in a condition to execute it. For wherever we can distinguish several points in any object, it must be divisible into so many parts.

We speak not, therefore, of a division practicable by our strength and skill, but of that which is possible in itself, and which the Divine Omnipotence is able to accomplish.

It is in this sense, accordingly, that philosophers use the word ‘divisibility:’ so that if there were a stone so hard that no force could break it, it might be without hesitation affirmed as divisible, in its own nature, as the most brittle, of the same magnitude. And how many bodies are there on which we cannot lay any hold, and of whose divisibility we can entertain not the smallest doubt? No one doubts that the moon is a divisible body, though he is incapable of detaching the smallest particle from it: and the simple reason for its divisibility, is its being extended.

Wherever we remark extension, we are under the necessity of acknowledging divisibility, so that divisibility is an inseparable property of extension. But experience likewise demonstrates that the division of bodies extends very far. I shall not insist at great length on the instance usually produced of a ducat*: the artisan can beat it out into a leaf so fine, as to cover a very large surface, and the ducat may be divided into as many parts as that surface is capable of being divided. Our own body furnishes an example much more surprizing. Only consider the delicate veins and nerves with which it is filled, and the fluids which circulate through them. The subtility there discoverable far surpasses imagination.

*A ducat is a gold coin used in Euler’s day.

The smallest insects, such as are scarcely visible to the naked eye, have all their members, and legs on which they walk with amazing velocity. Hence we see that each limb has its muscles composed of a great number of fibres; that they have veins, and nerves, and a fluid still much more subtile which flows through their whole extent.

On viewing with a good microscope a single drop of water, it has the appearance of a sea; we see thousands of living creatures swimming in it, each of which is necessarily composed of an infinite number of muscular and nervous fibres, whose marvellous structure ought to excite our admiration. And though these creatures may perhaps be the smallest which we are capable of discovering by the help of the microsope, undoubtedly they are not the smallest which the Creator has produced. Animacules probably exist as small relatively to them, as they are relatively to us. And these after all are not yet the smallest, but may be followed by an infinity of new classes, each of which contains creatures incomparably smaller than those of the preceding class.

We ought in this to acknowledge the omnipotence and infinite wisdom of the Creator, as in objects of the greatest magnitude. it appears to me, that the consideration of these minute species, each of which is followed by another inconceivably more minute, ought to make the liveliest impression on our minds, and inspire us with the most sublime ideas of the works of the Almighty, whose power knows no bounds, whether as to great objects or small.

To imagine that after having divided a body into a great number of parts, we arrive, at length, at particles so small as to defy all farther division, is therefore the indication of a very contracted mind. But supposing it is possible to descend to particles so minute as to be, in their own nature, no longer divisible, as in the case of the supposed monads; before coming to this point, we shall have a particle composed of only two monads, and this particle will be of a certain magnitude or extension, otherwise it could not have been divisible into these two monads. Let us farther suppose, that this particle, as it has some extension, may be the thousandth part of an inch, or still smaller if you will; for it is of no importance, what I say of the thousandth part of an inch may be said with equal truth of every smaller part. This thousandth part of an inch, then, is composed of two monads, and consequently two monads together would be the thousandth part of an inch, and two thousand times nothing, a whole inch; the absurdity strikes at first light.

The partisans of the system of monads accordingly shrink from the force of this argument, and are reduced to a terrible nonplus when asked how many monads are requisite to constitute an extension. Two, they apprehend, would appear insufficient, they therefore allow that more must be necessary. But, if two monads cannot constitute extension, as each of the two has none; neither three, nor four, nor any number whatever will produce it; and this complexity subverts the system of monads.

9th May, 1761.

Letters of Euler to a German Princess, Vol. II, Letter X

July 3, 2018

This is the fourth of eleven Letters of Euler I will rewrite and post on the subject of infinitesimals (the infinitely small), an idea that is fundamental to a good understanding of calculus. Click here to read the previous letter, which I posted over a year ago. Sorry, I’m a little slow on posting these!

Letter X. Of Monads.

When we talk, in company, on philosophical subjects, the conversation usually turns on such articles as have excited violent disputes among philosophers.

The divisibility of the body is one of them, respecting which the sentiments of the learned are greatly divided. Some maintain, that this divisibility goes on to infinity, without the possibility of ever arriving at particles so small as to be susceptible of no farther division. But others insist, that this division extends only to a certain point, and that you may come at length to particles so minute, that, having no magnitude, they are no longer divisible. These ultimate particles, which enter into the composition of bodies, they denominate simple beings, and monads.

There was a time when the dispute respecting monads employed such general attention, and was conducted with so much warmth, that it forced its way into company of every description, that of the guard-room not excepted. There was scarce a lady at court who did not take a decided part in favour of monads or against them. In a word all conversation was engrossed by monads, no other subject could find admission.

The Royal Academy of Berlin took up the controversy, and being accustomed annually to propose a question for discussion, and to bestow a gold medal of the value of fifty ducats on the person who in the judgment of the Academy has given the most ingenious solution, the question respecting monads was selected for the year 1748. A great variety of essays on the subject were accordingly produced. The president Mr. de Maupertuis named a committee to examine them, under the direction of the late Count Dohna, great chamberlain to the queen; who, being an impartial judge, examined with all imaginable attention, the arguments adduced both for and against the existence of monads. Upon the whole, it was found that those which went to the establishment of their existence were so feeble, and so chimerical, that they tended to the subversion of all the principles of human knowledge. The question was, therefore, determined in favour of the opposite opinion, and the prize adjudged to Mr. Justi, whose piece was deemed the most complete refutation of the monadists.

You may easily imagine how violently this decision of the Academy must irritate the partisans of monads, at the head of whom stood the celebrated Mr. Wolff. His followers, who were then much more numerous, and more formidable than at present, exclaimed in high terms against the partiality and injustice of the Academy; and their chief had well nigh proceeded to launch the thunder of a philosophical anathema against it. I do not now recollect to whom we are indebted for the care of averting this disaster.

As this controversy has made a great deal of noise, you will not be displeased, undoubtedly, if I dwell  a little upon it. The whole is reduced to this simple question, “Is the body divisible to infinity?” or in other words, “Has the divisibility of bodies any bound, or has it not?” I have already remarked as to this, that extension, geometrically considered, is on all hands allowed to be divisible infinitum; because, however small a magnitude may be, it is possible to conceive the half of it, and again the half of that half, and so on to infinity.

This notion of extension is very abstract, as are those of all genera, such as that of man, of horse, of tree, etc., as far as they are not applied to an individual and determinate being. Again, it is the most certain principle of all our knowledge, that whatever can be truly affirmed of the genus, must be true of all the individuals comprehended under it. If therefore all bodies are extended, all the properties belonging to extension must belong to each body in particular. Now all bodies are extended; and extension is divisible to infinity; therefore every body must be so likewise. This is a syllogism of the best form; and as the first proposition is indubitable, all that remains, is to be assured that the second is true, that is, whether it be true or not, that bodies are extended.

The partisans of monads, in maintaining their opinion, are obliged to affirm, that bodies are not extended, but have only an appearance of extension. They imagine that by this they have subverted the argument adduced in support of the divisibility in infinitum. But if body is not extended, I should be glad to know, from whence we derived, the idea of extension; for, if body is not extended, nothing in the world is, as spirits are still less so. Our idea of extension, therefore, would be altogether imaginary and chimerical.

Geometry would accordingly be a speculation entirely useless and illusory, and never could admit of any application to things really existing. In effect, if no one thing is extended, to what purpose investigate the properties of extension? But as geometry is, beyond contradiction, one of the most useful of sciences, its object cannot possibly be a mere chimera.

There is a necessity, then, of admitting, that the object of geometry is at least the same apparent extension which those philosophers allow to body; but, this very object is divisible to infinity: therefore existing beings, endowed with this apparent extension, must necessarily be extended.

Finally, let those philosophers turn themselves which way soever they will in support of their monads, or those ultimate and minute particles, divested of all magnitude, of which, according to them, all bodies are composed, they still plunge into difficulties, out of which they cannot extricate themselves. They are right in saying, that it is a proof of dulness to be incapable of relishing their sublime doctrine; it may however be remarked, that here the greatest stupidity is the most successful.

5th May, 1761.

Comparing Khan Academy’s “Procedures” to Shormann Math’s “Story” for Teaching High School Math

June 14, 2017

In a 2012 Education Week article, Justin Reich, an internet education specialist, wrote that Khan Academy’s math courses overemphasize procedure. In other words, Khan’s math video lectures explain the steps to solve a problem, but they don’t take time to explain the concept behind the steps. In the words of the author, “writing about mathematics, developing a disposition for mathematical thinking, demonstrating a conceptual understanding of mathematical topics are all more important than procedures.”

But, procedures ARE important, and sometimes, that is what you need. For example, if you are stuck on the side of the road with a flat tire, someone needs to know the steps required to fix the problem in as few steps as possible. You are not interested in the physics behind hydraulic jacks or who invented vulcanized rubber (Charles Goodyear). You have a crisis, and it requires a pragmatic solution. So, maybe you are studying for a big test like the SAT, and it’s in 2 weeks, and suddenly you realize there’s a concept you need to practice some more. This would be a time when Khan Academy might be helpful to you.

But, a good education isn’t really about pragmatism, about skimming through a subject, learning the bare minimum, so you can check it off your transcript or pass a standardized test. And then forget about it.

Shormann Math is different. Certainly, there are times when procedure is emphasized, like our step-by-step video solutions for every homework problem, for example. But there are more things, deeper things, that Shormann Math emphasizes that others, like Khan or Reich or the National Council of Mathematics Teachers either don’t, or won’t.

At the heart of mathematics is a story, an amazing story of the history of humans seeking to discover more about the world around them. And it’s a story that is best understood from a Christian foundation.

Here’s why. To his credit, in Khan Academy’s introductory Algebra 1 lesson, Sal Khan dives into the origins of algebra.  In describing the date of the first algebra book (820 A.D.), Khan makes a well-meaning, respectful attempt to distinguish the “religious” B.C. and A.D. from the “non-religious” common era descriptions of historical dates. Of course, the problem here is that Christianity is the only “religion” considered here. But Christianity is most definitely not a religion, a mere set of rules to keep or procedures to follow.

At its core, Christianity is about a relationship. And that’s a surprisingly hard truth for some to acknowledge. Christianity is about a relationship between God the Father, Son and Holy Spirit, between humans and God, and between humans and humans. Simply put, Christianity is about how this relates to that. But so is mathematics, which is not surprising since its normal for created things to reflect the attributes of their designers. Relationships always tell a story, over time. Which is why history matters in Christianity, and therefore in mathematics, too.

So, with Khan Academy, a student might feel connected to mathematics when they are finished, which is not a bad thing. With Shormann Math though, while our students are connecting to mathematics in measurable ways (see next post on results), we are also connecting them to the story behind mathematics.  And the story is that, throughout history, mathematics is a tool for studying the world around us. So, we give students the mathematical tools to use in their thinking about the world, and give them a chance to practice using them in a variety of situations they might encounter in their everyday lives. But we also tell them who discovered the tools, plus some interesting things about their life stories.

Everyone loves a good story! That the story of mathematics is largely missing from popular, secular math teaching methods like Khan Academy could partly explain why mathematics is often the least-liked, most dreaded subject of all. Overemphasizing procedure may get you an algebra credit, but it won’t necessarily develop the STEM and STEAM skills so often desired.

But what if story is included, so that students get to know the major players influencing modern mathematics? With Shormann Math, we are finding that telling the story of mathematics makes learning math more real, and in the end, easier. If students are inspired by the experiences of historical figures, or by what God’s word says about math, they are more likely to know what to do with the math tools they are becoming fluent with. And if Shormann Math students are more fluent than students using more secular and disconnected methods, then when the opportunity to use math comes along, Shormann Math students will likely be more prepared.

Comparing Khan Academy’s Mastery Approach to Shormann Math’s Fluency Approach for Teaching High School Math

May 25, 2017

This is the first in a series of posts comparing Khan Academy’shormann khan comparison memes online math courses to our new Shormann Math curriculum. Shormann Math is part of DIVE Math and Science.

When Sal Khan started tutoring his cousins in 2003 using digital whiteboard video lectures, my family’s small business was already in its third year of producing similar products. Since then, both Khan Academy and DIVE have continued to offer digital video lectures for learning mathematics and other subjects, leveraging the ever-improving array of digital content delivery methods. Today in 2017, both Khan Academy and DIVE offer self-paced eLearning math courses. So, while there are obvious similarities between the two, there are also some pretty big differences.

Khan’s Store-Bought Layer Cake vs. Shormann Math’s Homemade Pizza

To begin, it is important to understand that Khan Academy teaches a Common Core-based “layer cake” approach to high school math. Shormann Math, on the other hand, teaches an integrated approach pioneered in Europe and Asia (you know, the countries that always beat us on international math tests), and introduced to the United States by the late John Saxon. John Saxon believed in the common-sense idea that results, not methodology are what mattered most(we’ll explore Khan Academy vs. Shormann Math results in a later post).

With the layer-cake approach, high school math is taught in layers, beginning with Algebra 1. Geometry is next, then Algebra 2. Each course is typically covered in one school year.

With the integrated approach, students learn algebra and geometry together. For example, Shormann Math does not have a separate geometry course, because geometry is integrated into Algebra 1 and 2. A geometry credit is included in Shormann Algebra 1 and 2, so students can take 3 years to complete the two courses and be “on track.”

Using a food analogy, both a store-bought layer cake and a homemade pizza can be delicious. With a store-bought layer cake, everybody gets the same thing, which is not always a bad thing, but can be. With a layer cake, if you just like vanilla, you can focus on eating the vanilla and not the chocolate. Or vice-versa.

With a homemade pizza, at least the one my family has made for years, each bite is an integrated medley of cheeses, meats, and vegetables. It is unique, diverse, and anchored in an amazing story that originated on float trip adventures deep in the Alaskan wilderness. Our homemade pizzas are about more than pizza, just like our Shormann Math courses are about more than math.

homemade pizza

Shormann Math, like our family’s legendary pizza, is a savory recipe developed over time with proven ingredients.

From my experience, a layer-cake approach is good for reviewing a particular subject, or specific concepts within a subject. Our CLEP and AP test prep courses employ this method. In other words, the layer-cake approach is good for review, which means Khan Academy math is good for testing your math skills in a particular subject. Khan Academy can help you determine if you have mastered a particular concept for the short-term.

Shormann Math, on the other hand, can help you build fluency in mathematics, which means you develop mastery and you retain it for the long term because you keep using it. In the beginning of every Shormann Math course, we define mathematics as the language of science and a God-given tool for measuring and classifying pattern and shape. I am not sure how Khan Academy defines mathematics, as I couldn’t find a definition anywhere. When you learn a new language, you don’t just learn nouns for a year, then verbs for a year, etc. You learn a little of the basics of everything, then you start putting them into sentences, which you practice. And practice some more. And then you review some more. And practice some more.

Building on fundamentals is how you learn a language, or a sport, or an instrument, or just about anything that you, eventually, hope to excel at. Building fluency takes time. Up next, we’ll explore Khan Academy’s “math procedures” to Shormann Math’s “math story,” followed by real data from real Shormann Math students on how the fluency approach can turn a bad math student into a good one. Stay tuned and thanks for reading!

 

 

 

Letters of Euler to a German Princess, Vol. II, Letter VIII

May 22, 2017

This is the second of eleven Letters of Euler I will rewrite and post on the subject of infinitesimals (the infinitely small), an idea that is fundamental to a good understanding of calculus. Click here to read the previous letter.

Letter VIII. Divisibility of Extension in Infinitum

The controversy between modern philosophies and geometricians to which I have alluded, turns on the divisibility of body. This property is undoubtedly founded on extension, and it is only in so far as bodies are extended that they are divisible, and capable of being reduced to parts.

You will recollect that in geometry it is always possible to divide a line, however small, into two equal parts. We are likewise, by that science, instructed in the method of dividing a small line, ai, into any number of equal parts at pleasure, and the construction of this division is there demonstrated beyond the possibility of doubting its accuracy.

You have only to draw a line AI (plate II. fig. 23) parallel to ai of any length, and at any distance you please, and to divide it into as many equal parts AB, BC, CD, DE, etc. as the small line given is to have divisions, say eight. Draw afterwards, through the extremities A, a, and I, i the straight lines AaO, IiO, till they meet in the point O: and from O draw toward the points of division B, C, D, E, etc. the straight lines OB, OC, OD, OE, etc., which shall likewise cut the small line ai into eight equal parts.

Plate II, Fig 23, line AI parallel to line ai, each divided into 8 equal segments.

This operation may be performed, however small the given line ai, and however great the number of parts into which you propose to divide it. True it is, that in execution we are not permitted to go too far; the lines which we draw always have some breadth, whereby they are at length confounded, as may be seen in the figure near point O; but the question is not what may be possible for us to execute, but what is possible in itself. Now in geometry lines have no breadth*, and consequently can never be confounded. hence it follows that such division is illimitable.

*In Shormann Math, a line is defined as a widthless length, which is the same thing Euler is describing. In fact, all normal geometry courses define a line this way. The idea is that we are not concerned with how thick, or wide the line is. When you draw a line though, it has to have some thickness to it in order to be able to see it.

If it is once admitted that a line may be divided into a thousand parts, by dividing each part into two it will be divisible into two thousand parts, and for the same reason into four thousand, and into eight thousand, without ever arriving at parts indivisible. However small a line may be supposed, it is still divisible into halves, and each half again into two, and each of these again in like manner, and so on to infinity.

What I have said of a line is easily applicable to a surface, and, with greater strength of reasoning, to a solid endowed with three dimensions, length, breadth, and thickness. Hence is is affirmed that all extension is divisible to infinity, and this property is denominated divisibility in infinitum.

Whoever is disposed to deny this property of extension, is under the necessity of maintaining, that it is possible to arrive at last at parts so minute as to be unsusceptible of any farther division, because they ceased to have any extension. Nevertheless all these particles taken together must reproduce the whole, by the division of which you acquired them; and as the quantity of each would be a nothing, or cypher (0), a combination of cyphers would produce quantity, which is manifestly absurd. For you know perfectly well, that in arithmetic, two or more cyphers joined never produce any thing.

This opinion that in division of extension, or of any quantity whatever, we may come at last to particles so minute as to be no longer divisible, because they are so small, or because quantity no longer exists, is, therefore, a position absolutely untenable.

In order to render the absurdity of it more sensible, let us suppose a line of an inch long, divided into a thousand parts, and that these parts are so small as to admit of no farther division; each part, then, would no longer have any length, for if it had any, it would be still divisible. Each particle, then, would of consequence be a nothing. But if these thousand particles together constituted the length of an inch, the thousandth part of an inch would, of consequence, be a nothing; which is equally absurd with maintaining, that the half of any quantity whatever is nothing. And if it be absurd to affirm, that the half of any quantity is nothing, it is equally so to affirm, that the half of a half, or that the fourth part of the same quantity, is nothing; and what must be granted as to the fourth, must likewise be granted with respect to the thousandth, and the millionth part. Finally, however far you may have already carried, in imagination, the division of an inch, it is always possible to carry it still farther; and never will you be able to carry on your subdivision so far, as that the last parts shall be absolutely indivisible. These parts will undoubtedly always become smaller, and their magnitude will approach nearer and nearer to 0, but can never reach it.

The geometrician, therefore, is warranted in affirming, that every magnitude is divisible to infinity; and that you cannot proceed so far in your division, as that all farther division shall be impossible. But it is always necessary to distinguish between what is possible in itself, and what we are in a condition to perform. Our execution is indeed extremely limited. After having, for example, divided an inch into a thousand parts, these parts are so small as to escape our senses, and a farther division would to us, no doubt, be impossible.

But you have only to look at this thousandth part of an inch through a good microscope, which magnifies, for example, a thousand times, and each particle will appear as large as an inch to the naked eye; and you will be convinced of the possibility of dividing each of these particles again into a thousand parts: the same reasoning may always be carried forward, without limit and without end.

It is therefore an indubitable truth, that all magnitude is divisible in infinitum, and that this takes place not only with respect to extension, which is the object of geometry, but likewise with respect to every other species of quantity, such as time and number.

28th April, 1761.

Letters of Euler to a German Princess, Vol. II, Letter VII

May 18, 2017

This is the first of eleven Letters of Euler I will rewrite and post on the subject of infinitesmals (the infinitely small), an idea that is fundamental to a good understanding of calculus. I am rewriting them from a 1795 English translation, and will edit some of the awkward character usage (among other things, the first “s” used in any word actually looks like an “f”), but otherwise, for the most part, I will leave it unchanged. Additions and edits will be marked by braces, […].

Considered by scholars as the best mathematician in history, Euler’s influence is everywhere present in modern mathematics. Yet as smart as he was, he still took time to bring difficult concepts down to a level where a non-mathematician might learn some things. And, as you will see, defend the Christianity at the same time.

Although these posts from Letters of Euler are for students in my Shormann Calculus course(available Summer 2018), any curious prince or princess is welcome to read them, too! The idea Euler (and myself) is trying to convey is that any real object can be divided, and divided again. And again, until it is in such small parts (infinitesimals) we can’t see them. Nevertheless, they exist. But how? To understand that, let’s begin with Euler’s description of the properties of any real object, which he refers to as a body.  Enjoy!

Letter VII. The True Notion of Extension

I have already demonstrated, that the general notion of body necessarily comprehends these three qualities, extension, impenetrability, and inertia*, without which no being can be ranked in the class of bodies. Even the most scrupulous must allow the necessity of these three qualities, in order to constitute a body; but the doubt with some is, Are these three characters sufficient? Perhaps, say they, there may be several other characters, which are equally necessary to the essence of body.

*if a body has extension, that means you can measure it (length, mass, etc.); if it has impenetrability, that means you can feel it, which is possible with any solid, liquid or gas; if it has inertia that means it has the physical property of resisting a change in motion.

But I ask: were God to create a being divested of these other unknown characters, and that it possessed only the three above mentioned, would they hesitate to give the name of body to such a being? No, assuredly; for if they had the least doubt on the subject, they could not say with certainty, that the stones in the street are bodies, because they are not sure whether the pretended unknown characters are to be found in them or not.

Some imagine, that gravity is an essential property of all bodies, as all those which we know are heavy; but were God to divest them of gravity, would they therefore cease to be bodies? Let them consider the heavenly bodies, which do not fall downward; as must be the case, if they were heavy as the bodies which we touch, yet they give them the same name. And even on the supposition that all bodies were heavy, it would not follow that gravity is a property essential to them, for a body would still remain a body, though its gravity were to be destroyed by a miracle.

But this reasoning does not apply to the three essential properties mentioned. Were God to annihilate the extension of a body, it would certainly be no longer a body; and a body divested of impenetrability would no longer be a body; it would be a spectre, a phantom: the same holds as to inertia.

You know that extension is the proper object of geometry, which considers bodies only in so far as they are measurable. [Geometry does not consider impenetrability and inertia.] The object of geometry, therefore, is a notion much more general than that of body, as it comprehends not only bodies, but all beings simply extended without impenetrability, if any such there be. Hence it follows, that all the properties deduced in geometry from the notion of extension must likewise take place in bodies, in as much as they are extended; for whatever is applicable to a more general notion, to that of a tree, for example, must likewise be applicable to the notion of an oak, an ash, an elm, etc. And this principle is even the foundation of all the reasonings in virtue of which we always affirm and deny of the species,  and of individuals, every thing that we affirm and deny of the genus.

There are however, philosophers, particularly among our contemporaries, who boldly deny, that the properties applicable to extension, in general, that is, according as we consider them in geometry, take place in bodies really existing. They allege that geometrical extension is an abstract being, from the properties of which it is impossible to draw any conclusion, with respect to real objects: thus, when I have demonstrated that the three angles of a triangle are together equal to two right angles, this is a property belonging only to an abstract triangle, and not at all to one really existing.

But these philosophers are not aware of the perplexing consequences which naturally result from the difference which they establish between objects formed by abstraction, and real objects; and if it were not permitted to conclude from the first to the last, no conclusion, and no reasoning whatever could subsist, as we always conclude from general notions to particular.

Now all general notions are as much abstract beings as geometrical extension; and a tree, in general, or the general notion of trees, is formed only by abstraction, and no more exists out of our mind than geometrical extension does. The notion of man in general is of the same kind, and man in general no where exists: all men who exist are individual beings, and correspond to individual notions. The general idea which comprehends all, is formed only by abstraction.

The fault which these philosophers are ever finding with geometricians, for employing themselves about abstractions merely, is therefor groundless, as all other sciences principally turn on general notions, which are no more real than the objects of geometry. The patient, in general, who the physician has in view, and the idea of whom contains all patients really existing, is only an abstract idea; nay the very merit of each science is so much the greater, as it extends to notions more general, that is to say, more abstract.

I shall endeavor, by next post, to point out the tendency of the censures pronounced by these philosophers upon geometricians; and the reasons why they are unwilling that we should ascribe to real, [measurable] beings, that is, to existing bodies, the properties applicable to [measurement] in general, or to abstracted [measurement]. They are afraid lest their metaphysical principles should suffer in the cause.

25th April, 1761.