If one subtracts a positive number from a negative number, the process is still subtraction. For example, -3 minus 7 is -10. On the other hand, subtracting a negative number from a positive number is equivalent to addition.
Just as subtracting a negative is addition, adding a negative is subtraction. The process of adding a negative is the same as subtracting a positive number from another positive number. Whenever one subtracts a positive number from any other number, it remains subtraction and cannot increase the value of the resulting number. Adding a negative number to another negative number decreases its value further.