This word-use mistake has become surprisingly frequent in novels and stories I’ve read.  Although the concept of viewing life as a mathematical problem can work, the following statement is incorrect.

“The calculus changes when Harold is accused of murder.”

 

Calculus – a system of calculation using special symbolic notations.

I hated calculus class because I could never make the connection between the use of symbols and any real life problem.

Calculus requires a solid foundation in basic math.

 

Equation – a state of being equated; equality or balance; an element in a complex whole.

When Lynne’s mother left, the equation that represented family changed forever for the girl.

If you intend to become a dentist, equestrian training doesn’t figure into your education equation.

 

Here’s another look at Calculus and Equation.

Wrong:

Roger figured out the calculus of his chances for a date with Edita.

There was no equation for why Edita accepted Roger’s invitation to go out for coffee.

Right:

The only way to determine where the quark will appear on the timeline is through the use of advanced calculus.

The cops had to consider the new piece to their equation when they discovered a second bloody weapon covered with fingerprints that didn’t match those of their suspect.

Different branches of mathematics use specific systems of calculus to solve the equations created by scientists in their quest to understand the universe.

 

When you’re not sure which word to use, remember that calculus in a specific system of symbols and notations that mean something to the user.  And an equation is a problem into which you plug pieces—numbers, symbols, notations, clues—in order to find an answer.