Why is differential calculus often presented before integral calculus?

Why is differential calculus often presented before integral calculus?

Note: I'm still learning calculus at the moment.

It seems that many elementary calculus texts describe differential calculus before integral calculus. They start with an informal intuition into the concept of a limit and how to calculate various limits. They then go on to describe the derivative via physical applications and/or the tangent/secant line approach. To me it seems that the integral would be more intuitive to understand first, and then limits and derivatives. To the best of my knowledge, this is also how calculus was historically developed. Is there a particular reason for presenting the derivative before the integral in elementary calculus?

• All of the first calculus textbooks I know treat differential calculus before integral (L'Hospital, Bernoulli, Euler). With Leibniz notation it also seems clear why: differentials appear in $\int y dx$. Jul 6 '21 at 5:57
• b/c Antiderivatives require derivatives.
Jul 6 '21 at 11:43
• Can you add some justification for the claim that this is also how calculus was historically developed? As far as I know, integration theory was not developed much before differentiation was introduced, but I certainly don't know all the facts, and I'm curious to know. Jul 6 '21 at 17:09
• @MichałMiśkiewicz I recall that Hersh and Davis asserted something like "the integral part of calculus was known to the ancients", in the sense that ancient Greek mathematics used limits of sums to compute areas and volumes, which is pretty close to the way we'd do it using integrals now. Of course the notation and conceptualisation were rather different, but as the results are the same, it seems a not unreasonable claim to make. Of course there was then a millennia-long gap before Newton and Leibniz related the (also ancient) work on derivatives to integrals. Jul 7 '21 at 10:11
• I found derivatives a LOT easier than integrals. Jul 7 '21 at 14:40

David Bressoud has a 2019 book that argues for teaching integration before derivatives, and only later teaching limits, partly because that matches the way that the ideas developed historically: "Calculus Reordered: A History of the Big Ideas".

• I just purchased this book. I think the preface answers my question: "How did we wind up with a sequence that is close to the reverse of the historical order: limits first, then differentiation, integration, and finally series? The answer lies in the needs of the research mathematicians of the nineteenth century who uncovered apparent contradictions within calculus." I can't quote the entire preface here, but it describes this more in detail, and it also makes a good argument for why we might want to teach calculus via integration first, then differentiation, series, and finally limits.
– user13234
Jul 12 '21 at 5:20

While there are no theoretical difficulties with developing integration first ("from scratch" measure theory books demonstrate this), it presents some pedagogical challenges.

Most problems in existing Calculus courses have "closed form" solutions. It is rare to just set up a problem and then numerically evaluate. The primary tool available for exact calculation of definite integrals is the Fundamental Theorem of Calculus. Finding $$\int_0^1 x^5 \textrm{d}x$$ can be done numerically or exactly using excruciating Riemann sum calculations. We like to know that $$\frac{d}{dx} x^6 = 6x^5$$ before covering integration so that this integral can be evaluated exactly using the fundamental theorem.

I personally think it would be a better story if we taught integration first, got practice setting up all kinds of integrals to solve practical problems, and used numerical approximation as our only evaluation tool. This would drive home what the definite integral IS. Then do differential calculus in all of its glory. Then the FTOC would actually be surprising and useful (Wow! Now we can calculate these integrals exactly instead of just approximating!). As it is, most students think the FTOC is the definition of the definite integral, which is unfortunate.

• Another issue is the ordering of corequisite courses. A student taking physics at the same time might need to understand velocity as the derivative of position before they get to integrals later. So making a change in the "standard curriculum" forces potentially unwelcome changes to courses in other departments. There is just a ton of institutional inertia to doing anything different with a calculus course. Jul 6 '21 at 14:17
• You still have to do limits first though if you want real integral calculus and not just numerical math. Also limits that are much much harder than anything calc students normally cover.
– DRF
Jul 6 '21 at 18:37
• Also just the definition of a Riemann integral is pretty hard. I realize that calc students don't usually do proper proofs/definitions anyway, but you need a (proper) generalized definition of a limit if you want to define a Riemann integral. My experience that your normal calc student never even understands the basic limit definition. Which I think is another reason the order is what it is. You never actually learn differential calculus you learn a new kind of arithmetic.
– DRF
Jul 6 '21 at 18:41
• @DRF (cont.) going from about $100$ to $50$. Also, the average mark on the first midterm was only about $20$%! The course continued to teach derivatives and then, near the end, showed with the FTC that, for most cases, integrals can, at least in theory, be calculated as anti-derivatives. Interestingly, I guess because they didn't want to bell-curve too much or fail too many students, the final exam had very few questions covering the first part of the course, with most of it being instead about derivatives & calculating standard integrals. Jul 6 '21 at 20:38
• @user615 I agree this argument is not excruciating at all for us, but I think it would require at least a 50 minute lecture to reach 1/4 of the average freshman calculus population. You may also be interested in this: mathoverflow.net/questions/114738/… Jul 8 '21 at 13:26

One issue is that for differentiation, you can find the derivatives of so-called "elementary functions" (e.g. powers, exponentials, logarithms, trig functions) directly from the definition of a limit, and there are then standard ways to find the derivatives of an expression knowing the derivatives of its component parts (e.g. the product and quotient rules, function-of-a-function, etc.)

Therefore it is straightforward to generate a large number of "textbook exercises" of graded difficulty.

On the other hand, most "simple-looking functions" do not have closed-form integrals, and the easiest way to find a set of basic functions that do have closed form integrals is to recognize that "the function you want to integrate looks like a derivative that you already know".

In fact many of the so-called "special functions" in mathmematics are *defined" as the integral of a simple-looking function (e.g. the gamma function, which generalizes the idea of a factorial for non-integer values).

Of course as other answers have said, if you taught integration using only numerical methods as an initial way to evaluate integrals, that problem does not exist, but (at high school or university level) most students will not have much if any understanding of numerical methods, and therefore there are too many possibilities for "garbage-in garbage out" exercises where students have no way to check their work.

Typing formulas into Wolfram's integral evaluator isn't "learning math" - and it isn't even an interesting task, unless you are going to do something interesting with the output.

Because:

https://xkcd.com/2117/

The text I know of that does integration first is: Apostol, Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra.

An advantage of using this for top-rate incoming university students is that they do not think "I already know this" and tune out [as they may do when the course begins with differentiation].

• I just looked at the table of contents, and I find it interesting that continuity is treated after Riemann integrability. Jul 6 '21 at 14:57
• Great point! I think teaching the easy error bound on the Riemann sum (with equal width rectangles) in this case is important. Jul 7 '21 at 10:19

I think one of the main reasons for the ordering, limits-> derivatives -> integrals is that it follows in order of difficulty in some sense of the word.

In reality the situation is more complex, but if you start with the minimal (read $$\epsilon$$-$$\delta$$) definition of a limit it's fairly straightforward. It's also almost essential for even a semi rigorous treatment of both differential and integral calculus.

Differentiation comes pretty much next in complexity. In reality the basic version (assuming stuff you have is almost everywhere $$C^\infty$$) is actually quite a bit easier than limits, but since (it looks as if) you're using limits to calculate it, it's more complex. At the same time derivatives are important for a lot of other things you want the students to be learning, mainly basic physics, where you get differential equations at every corner.

Integration is by far the hardest both in terms of students understanding and actual computation. Unlike differentiation where (mostly) anything that can be written neatly has a neat (read made up of elementary functions) derivative, most integrals don't actually have a closed form solution. With "most" here meaning many of the ones students can think of.

All in all, this order is in many ways natural, progressing from easier to harder and building on previously learned material. In reality integration both 2d and 3d is a lot more complex than derivatives. Both in terms of the limits employed (you have to take a limit over partitions, so you need a new notion of limit) and the idea that's it's "finding the area under the curve" is actually surprisingly complex since you don't actually know what "area" is until you come up some version of integration.

I'd like to comment on why, indeed, it would be reasonable to present the subject with integrals first... (which is not what is done, nearly universally, I understand).

In particular, I'd argue that the notion of "derivative" is more sophisticated than "area under a curve". This includes the subtlety of "instantaneous rate of change". Yes, people'd been thinking about this a long time (cf. Zeno's paradoxes).

But/and, yes, a fundamental reason for the success of "calculus" as a very basic mathematical gadget is the fundamental theorem of calculus, giving explicit and elementary (indefinite) integrals for many interesting functions. Explicit (elementary) expressions obviously allow many more manipulations and experimentation than subtler "estimates".

For that matter, the first really rigorous results about differential equations used conversion of differential equations to integral equations, and invocation of theorems about compact operators. (See Volterra, Hilbert, Schmidt.)

In my own experience, I did think it was charming that slopes to polynomial curves could be exactly determined, but it was really amazing that areas under such graphs could be precisely (not just numerically) determined, and in forms that were astonishingly simple.

As with a huge number of the "why do we do this order" questions, or the "why don't we teach real analysis before calculus" questions, they seem to tacitly assume that the order of teaching is based on philosophical explanation or even formal mathematical proof. WRONG!

This is NOT the reason why instruction is structured the way it is. It is structured based on imperfect beings that learn harder subjects after easier ones, because that works better pedagogically. Instruction is a maximization problem of time, brains, etc. To get the most sense pounded into skulls within the practical limits that pertain in the practical world. And in the case of integration, it is harder than differentiation (going backwards) and makes more sense afterwards. So. Practical pedagogy uber theoretical explication.

• I do not see any pedagogical obstacles to an integration first presentation. In some ways (mentioned in other answers) integration is conceptually easier. I think the barriers are mostly institutional inertia rather than based in the relative difficulty of the topics. Your claim that integration is the inverse of differentiation is the same mistaken belief that many students have: that the definite integral is defined by the Fundamental Theorem rather than by Riemann sums. You do not need the derivative to study integration. Jul 7 '21 at 15:42
• @StevenGubkin: Explaining the geometric meaning of integration is easier, yes. But doing integration is not easier, conceptually or practically. Integration is not defined as the inverse of differentiation, but performing the inverse of differentiation is a useful method for performing integration. Jul 7 '21 at 20:12
• @BenVoigt Numerical integration is just multiplying and adding repeatedly. Almost all integrands do not have "closed form" antiderivatives, so the illusion that the antiderivative is useful for computation is ONLY an illusion. Better to be honest, teach the numerics, and bound the error. Jul 7 '21 at 20:40
• You seem to be operating under the illusion that there's any kind of consistency between integration buttons on calculators. In fact, the only calculators I'm aware of with any numerical integration features also have computer algebra systems (how else do you input the expression to be integrated?) and those will prefer an algebraic integration and only perform a sum if algebraic methods fail. Jul 7 '21 at 20:47
• @StevenGubkin numerical integration is only simple at the conceptual level, with simple integrands. Too often do I come across practical quadrature problems that require a change of variables, Taylor expansion, or some other transformation in order to avoid numerical instability or overflow (e.g. evaluation of the integrand near removable singularities; computing improper integrals). And this already involves derivatives. Jul 8 '21 at 10:46