The discourse markers “on the contrary” and “to the contrary” convey the same sense—that something is in opposition to what’s expected—but they are generally not interchangeable in usage.
When something has just been said, “on the contrary” is commonly used to emphasize that the opposite of that statement is true. Example: “The candidates for vice chairman aren’t an exciting choice at all
; on the contrary, they just douse the enthusiasm of intelligent voters.”
On the other hand, “to the contrary” is usually used by a speaker or writer to alert the audience that what’s to be said next is the opposite of what has just been said. Example: “Despite several compelling testimonies
to the contrary, the accused was convicted of homicide.”
From a sentence structure standpoint, note that in the case of “on the contrary,” a complete statement or an entire argument is typically made first (“the candidates for vice chairman aren’t an exciting choice at all”). The discourse marker “on the contrary” is then inserted, followed by another complete statement to the contrary (“it just douses the enthusiasm of intelligent voters”). In short, “on the contrary” is commonly used as a conjunctive adverb between two coordinate parallel clauses.
In the case of “to the contrary,” the discourse marker is typically used to mark a contrast between a particular noun or noun phrase just mentioned (“several compelling testimonies”) and a statement that follows it (“the accused was convicted of homicide”). In such sentence constructions, “to the contrary” forms part of a prepositional phrase modifying a sentence. (Note that the example sentence given in this case can be reconstructed as “The accused was convicted of homicide despite several compelling testimonies
to the contrary,” showing that it’s actually only one clause with the preposition “despite” introducing the modifying phrase.)
In conversational English, however, this distinction between the usage of “on the contrary” and “to the contrary” is sometimes lost, as in the following conversation:
Woman A: You seem to be so agitated. Have you lost anything?
Woman B: On the contrary [to the contrary], I’m very happy! I just got the big job I applied for!
When something that big happens to people, we really can’t fault them that much for forgetting the niceties of English grammar; hence, the blurring of the difference between “on the contrary” and “to the contrary” in the conversational idiom is perhaps understandable.
