# Y=MX+B **URL:** \ **Category:** Factual Questions\ **Created:** [December 6, 2000, 11:08pm UTC](https://boards.straightdope.com/t/y-mx-b/44402 "2000-12-06T23:08:11Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![sk8rixtx](https://avatars.discourse-cdn.com/v4/letter/s/858c86/32.png) [@sk8rixtx](https://boards.straightdope.com/u/sk8rixtx)\ **Post date:** [December 6, 2000, 11:08pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/1 "2000-12-06T23:08:11Z")
In the algebraic equation: y=mx+b Why does the letter “m” represent the slope? Couldn’t “s” do just as good a job. It seems that it would be easier to remember. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [December 6, 2000, 11:12pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/2 "2000-12-06T23:12:10Z")
Maybe it is the ‘magnitude’ of the the difference between values of y. That was a WAG, but then why is the y-intercept b? Me, I’m just glad there’s something out there that makes more sense than the ‘standard’ form. ---
**Author:** ![Jman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jman/32/4416_2.png) [@Jman](https://boards.straightdope.com/u/Jman)\ **Post date:** [December 6, 2000, 11:12pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/3 "2000-12-06T23:12:22Z")
Because ‘s’ looks like 5. A lot of people would look at the equation and think they just hadn’t solved the intercept yet. y=5x+b. Jman ---
**Author:** ![sk8rixtx](https://avatars.discourse-cdn.com/v4/letter/s/858c86/32.png) [@sk8rixtx](https://boards.straightdope.com/u/sk8rixtx)\ **Post date:** [December 6, 2000, 11:35pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/4 "2000-12-06T23:35:08Z")
> [@](#): > > \*Originally posted by Derleth \* > **…why is the y-intercept b?** I’m not sure why the y intercept is “b”, but one way to think of it is: “b” is the first letter of “bi”. “Bi” rhymes with “y”, as in y-intercept. Mneumonic device. The only thing is, I can’t make sense of where “m” was derived from, and how to assess it to this equation. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [December 6, 2000, 11:35pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/5 "2000-12-06T23:35:44Z")
> [@](#): > > \*Originally posted by Derleth \* > \*\*why is the y-intercept b? \*\* I have seen **a** used as the x-intercept, so **b** makes sense for the y-intercept. About **m** , I don’t know, but it could be from a foreign language, such as French, German, or Latin. ---
**Author:** ![Cabbage](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@Cabbage](https://boards.straightdope.com/u/Cabbage)\ **Post date:** [December 6, 2000, 11:47pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/6 "2000-12-06T23:47:46Z")
Actually, no one is really certain why “m” is used for slope. The two most common theories I’ve seen are: 1. It stands for “montrer/monter” which is French for “to climb” (I’ve seen this word spelled both ways, I don’t speak French and don’t know which is correct). 2. It stands for “modulus of slope”. Just theories, though; by no means are these definitive answers. You can find more speculation [here](http://forum.swarthmore.edu/dr.math/problems/m.for.slope.html). ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [December 7, 2000, 12:08am UTC](https://boards.straightdope.com/t/y-mx-b/44402/7 "2000-12-07T00:08:46Z")
What **Cabbage** said. I found a neat site called [Earliest Use of Various Mathematical Symbols](http://members.aol.com/jeff570/mathsym.html). On their [geometry page](http://members.aol.com/jeff570/geometry.html) they say > [@](#): > > The earliest known use of m for slope is an 1844 British text by Matthew O’Brien entitled A Treatise on Plane Co-Ordinate Geometry. . . . > > It is not known why the letter m was chosen for slope; the choice may have been arbitrary. John Conway has suggested m could stand for “modulus of slope.” One high school algebra textbook says the reason for m is unknown, but remarks that it is interesting that the French word for “to climb” is monter. However, there is no evidence to make any such connection. Descartes, who was French, did not use m. In Mathematical Circles Revisited (1971) mathematics historian Howard W. Eves suggests “it just happened.” ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [December 7, 2000, 1:04am UTC](https://boards.straightdope.com/t/y-mx-b/44402/8 "2000-12-07T01:04:57Z")
My advice is to not even try and figures stuff like this out. Great ignorace-fighting technique, I know, but in my last physics class, a friend and I went through every letter in the English and Greek alphabets and were able to think of something each one represented. Capital _and_ lowercase, BTW. Many had two or three or more meanings. After a while, it’s just a matter of “which letter haven’t we used in a while?” ---
**Author:** ![KJ](https://avatars.discourse-cdn.com/v4/letter/k/b2d939/32.png) [@KJ](https://boards.straightdope.com/u/KJ)\ **Post date:** [December 7, 2000, 1:27am UTC](https://boards.straightdope.com/t/y-mx-b/44402/9 "2000-12-07T01:27:18Z")
If you make the slope S and the y-intercept i, it becomes y = sx + i, which looks like y = 5x + 1. Probably not the only reason, but it might be one of them. ---
**Author:** ![jbird3000](https://avatars.discourse-cdn.com/v4/letter/j/aeb1de/32.png) [@jbird3000](https://boards.straightdope.com/u/jbird3000)\ **Post date:** [December 7, 2000, 2:56am UTC](https://boards.straightdope.com/t/y-mx-b/44402/10 "2000-12-07T02:56:51Z")
b stands for base (at least in french). ---
**Author:** ![mnemosyne](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mnemosyne](https://boards.straightdope.com/u/mnemosyne)\ **Post date:** [December 7, 2000, 3:20am UTC](https://boards.straightdope.com/t/y-mx-b/44402/11 "2000-12-07T03:20:07Z")
And the term **Cabbage** was refering to is monter (to climb). Mont_r_er means to show. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 7, 2000, 10:03am UTC](https://boards.straightdope.com/t/y-mx-b/44402/12 "2000-12-07T10:03:50Z")
> [@](#): > > \*\*In the algebraic equation: > > > [@](#): > > > > y=mx+b > > Why does the letter “m” represent the slope?\*\* OK I’ve got to ask, is this really the standard letter denoting the slope, and to whom? American textbooks? I don’t think I’ve ever seen this used - y=ax+b seems a more natural choice of letters to me, but **s** is also as good as any. ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [December 7, 2000, 12:42pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/13 "2000-12-07T12:42:41Z")
> [@](#): > > \*Originally posted by sk8rixtx \* > \*\*In the algebraic equation: > > y=mx+b > > Why does the letter “m” represent the slope? > \*\* In Ireland in both school and university it was “y=mx+c”, where c stands for “constant”. Can’t help with “m” though. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [December 7, 2000, 1:41pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/14 "2000-12-07T13:41:28Z")
> [@](#): > > \*Originally posted by Jman \* > \*\*Because ‘s’ looks like 5. A lot of people would look at the equation and think they just hadn’t solved the intercept yet. y=5x+b. > > Jman \*\* I think you’re correct. For the reason you stated, I hate it when “S” is used in any equation. The Laplace Transform comes to mind; when doing those, I always use a “$” in place of the “S”. Same goes for model numbers on equipment. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [December 7, 2000, 1:58pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/15 "2000-12-07T13:58:23Z")
> [@](#): > > \*Originally posted by KJ \* > \*\*If you make the slope S and the y-intercept i, it becomes y = sx + i, which looks like y = 5x + 1. Probably not the only reason, but it might be one of them. \*\* Kinda sexy, though. Might improve the image. ---
**Author:** ![c\_goat](https://avatars.discourse-cdn.com/v4/letter/c/f4b2a3/32.png) [@c\_goat](https://boards.straightdope.com/u/c_goat)\ **Post date:** [December 7, 2000, 2:41pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/16 "2000-12-07T14:41:47Z")
I just figured “s” was used for something else. Doesn’t s have another meaning in math? (I can’t remember any equations using it). I thought they tried to use different letters so you would know which equation you were dealing with. ---
**Author:** ![Andy](https://avatars.discourse-cdn.com/v4/letter/a/aeb1de/32.png) [@Andy](https://boards.straightdope.com/u/Andy)\ **Post date:** [December 7, 2000, 3:09pm UTC](https://boards.straightdope.com/t/y-mx-b/44402/17 "2000-12-07T15:09:26Z")
S represents entropy in some equations.