You'd think that pro- and con- are opposites, right?

And yet a protest over a matter is pretty much the same thing as a contest over it, and to protest it is to contest it.

How did that happen?

I am sure someone else will have more knowledge on this, wordnerd. But it is an interesting question. In looking up "con," it can mean "with" or "together," though it then says to see "com." "Con" can also be short for the Latin "contra" meaning "against." "Pro" means "for" or "before."

When I looked up "contest," it seemed to say it came from "com" and "testis." "Protest" comes from "pro" and "testis."

Is it that the root for "con" isn't the "contra" meaning, but it is the "com" meaning? That would make sense. However, I surely am not the Latin scholar here!

'Pro and con' is a mediaeval abbreviation for 'pro and contra', where contra = 'against' and is constrasted wih pro = 'for': it's not the prefix con-, which never means this.

The Latin contra 'against' is related to the prefix com/con/co 'with', but in a rather semantically opaque way. They're certainly not equivalent or close.

To contest is in origin to take issue with witnesses; to protest is to proclaim before (pro) witnesses.