Why call slope m has been a question that has been researched by math historians but has not been answered definitively yet.
Erica Voolich
Many people have been taught that it comes from the French, "monter", to climb. I think this is an "urban legend".
John Conway
Former Mathematics book writer, M. Risi answered "In our system, the first letters of the alphabet, a, b , c... represent the constants, the last letters, x, y, z represent the unknown variables and the middle letters, m, n, p... represents the parameters. When we started the explanations of slope, it was in studying the first degree equation: y = mx + b. x and y were the variables, b was fixed and considered as a constant, and what was appended to the coefficient of x as its value varied. So it was a parameter and that is why we used m."
André Deschênes
But M. Risi plainly wasn't the first person to use "m" in this connection.
on this continent the typical form is y = mx + b, whereas in England and in "the" Continent it is y = mx + c. The latter form still seems to me to be more natural, since this "c" is like the arbitrary constants in indefinite integrals, and so it will probably be very hard to date. But the "b" usage probably originated with the author of a particular influential North American textbook.
John Conway
According to one of the most eminent mathematics historians in the US who has researched the topic, Professor Frederick Rickey, Bowling Green University, Ohio, we do NOT know why m was used for slope in the slope/intercept form of the equation. Book authors who give the French connection are WRONG. Professor Rickey says there is absolutely no proof for the French connection.
Karen Dee Michalowicz
Yes, in 1990 I did write a brief note in the HPM Newsletter about the origin of the word slope. Since then I have pushed the first use of the word (that I know of) back to 1850. Before that phrases such as "the
tangent of the angle between the line and the x-axis" were used. I take this as evidence that the concept of slope had not crystallized and so name was attached to it. Both the word "slope" and the use of the letter "m" seem to have originated in the USA.
Fred Rickey
I just wanted to say that I think of m as standing for "move" and b for "begin." This relates to the way you graph linear equations by hand. You can use the b value to plot the "beginning" point (0,b). Then the m value instructs you where to "move" from point (0,b) to plot the next point, thus giving you the line for the equation.
Robby "Math-freak" Grant
http://mathforum.org/library/drmath/view/52477.html
