"Pro" means for, and "con" means against; "the pros and cons" are the reasons for and against doing something. Example: "Should we do it or not?" Answer: "First let's look at the pros and cons." Before you decide to do it or not, you should try to understand the reasons for doing it (the pros) and the reasons against doing it (the cons). Example: "Before we decide, let's be sure we understand the pros and cons." A "pro" is a reason to do something; a "con" is a reason to not do it. Example: "I've considered the pros and cons and I've decided: it is going to be expensive, but I still want to go to college." The pros and cons are the good and bad aspects of some thing.