Because it can be derived from other mathematical rules and theorems which can be derived from other rules and theorems etc etc until you're back to addition and subtraction. BOMBDAS was just made up on the spot.aDuck said:Sigh... Don't know why I'm asking this, but what is the difference between current mathematical convention and maths? Because if you're splitting hairs with this, then why dont you say that all maths that we use now is current mathematical convention and shun anyone who calls it maths?