For those who have read multiple math books you like me have probably encountered the term "the calculus" and you know what I'm talking about.

For example the derivative of something is being taken so the book will phrase it as:

"From the calculus we can take the derivative of x with respect to y in order to get its slope at point P....."

But when we talk about algebra the books only ever say something like:

"Using algebra we can transform the equation into the form Mf(x,y) + Ng(x,y) = 0"

"Using algebra" would be the term used and not "the algebra"

also same with geometry no one ever says "the geometry".

But why do they often say "the calculus"? Why is not just "calculus"?