Q: If I can disagree with you, why can’t I agree against you?
A: Obviously, the “dis-“ prefix in “disagree” negates the verb “agree.” So why can’t “against” negate it as well?
The answer is that “against” doesn’t work in quite that way.
The word “against,” which generally functions as a preposition, has many meanings, according to the Oxford English Dictionary. We’ll give a few examples.
“Against” can mean in contact with or supported by (“leaning against a tree” … “looks well against a dark background” … “nestled against his shoulder”).
But it can also mean in collision with (“the plate broke against the sink”); in an opposite direction (“against the tide” … “against the grain”); or contrary to (“against my wishes”).
In addition, “against” can mean unfavorable (“her appearance was against her”); in competition with (“a race against the clock”); or opposed (“he’s against it”).
In other meanings, “against” can imply resistance or protection (“I’ll defend you against harm”). And you can bet “against” something, weigh one thing “against” another, or save your pennies “against” a rainy day.
But the sense that comes closest to a negation means in opposition to (as in “vote against” … “speak out against”).
And this sense of “against” is often used, the OED says, in “expressing the adverse bearing of many verbs and nouns of action.”
In other words, “against” can be used with many action words—those that have the potential to be used in a negative way—to bring out that negativity.
The OED goes on to give these examples of such verbs: “to legislate, protest, argue, testify; offend, sin; cry out, rage, inveigh, exclaim.”
And it gives these examples of such nouns: “a law, proclamation, declaration, protest, argument, objection, resolution, action, proceeding, accusation, complaint, evidence; sin, offence; hostility, outcry, feeling, prejudice, rage, anger, animosity, bitterness, grudge, etc.”
Note that, as the OED says, these are words of “adverse bearing”—words that are capable of being used in a negative way. The verb “agree” isn’t one of them. It’s simply too agreeable.
So while you could “testify against” someone, you couldn’t “agree against” that person.
We hope this answers your question. And if you’re still confused, please don’t hold it against us!
Check out our books about the English language