In math, the terms successor and predecessor refer to the numbers directly after or directly before a given number, respectively. To find the successor of a given whole number, add one to the given number. To find the predecessor of a given whole number, subtract one from the given number.
Suppose that the given number is 18. Its successor is 19, and its predecessor is 17. If the given number were 226, it would have a successor of 227 and a predecessor of 225. Additionally, if x is the successor of y, then y is the predecessor of x. For instance, 80 is the successor of 79, so therefore 79 is the predecessor of 80.
The terms successor and predecessor apply only to whole numbers—that is, zero, one, two, three and so on; they do not apply to fractions, decimals or negative numbers. Every whole number has a successor. With the exception of zero, every whole number also has a predecessor.