Back into the impact-as-verb morass. Commenter Amy on Mark Liberman’s latest “word rage” posting on Language Log:
Whenever I complain about people using impact as a verb, I clarify the misuse thusly: The only thing you can impact is a retina. Otherwise, you have an impact ON it.
This is no clarification, and no explanation. It’s just a restatement of the proscription in other words. It’s a non-argument, of the form:
You can’t [= mustn't, may not] say X to convey meaning M because you have to say Y instead.
What makes it a non-argument is that in the real world there are plenty of (roughly) alternative ways of “saying the same thing”, so there’s no logical reason why X and Y couldn’t both be available for conveying M. So saying that you have to say Y to convey M is just another way of asserting (baldly) that X is not available for this purpose — that is, asserting that you mustn’t say X.
This sort of circular non-clarification of usage proscriptions is, I think, not at all uncommon, though most proscriptions aren’t framed as explanations (with because or other causal wording), but as straightforward directives:
Don’t say X to convey meaning M; say Y instead.
It might be an interesting (though dismaying) exercise, for, say, an otherwise empty weekend, to collect spuriously causal formulations of proscriptions.
There’s more to say about this brief passage from Amy’s comment.
I’ve suggested replacements for Amy’s original can’t, to bring out the normative character of her account. Obviously, rather a lot of people can (and do) use the verb impact for ‘affect’ and a cluster of related figurative meanings. Amy is telling them not to, or withholding permission for them to. I don’t know who died and made her queen.
Then there’s there’s the suggested replacement, with the noun impact: “have an impact on”. This is cute (even ironic), since early critics of the verb impact used figuratively also mostly objected to the noun impact used figuratively (meaning roughly ‘an effect’), instead of in the historically older sense (roughly ‘a collision’). See MWDEU for details.
Finally, there’s the weirdness about retinas: “The only thing you can impact is a retina.” This is news to me.
To start with, the occurrences of “impact the retina” you can google up include many with the meaning ‘affect the retina’, mostly in medical contexts dealing with unpleasant effects on the retina of various diseases and conditions; that’s figurative impact. But there are also others in which impact means roughly ‘impinge on’, and what impacts the retina is specifically light waves; that’s a fairly early sense, roughly ‘collide with’, but by no means restricted to retinas and/or light waves. In fact OED2’s entry for the verb impact has no cites with retinas being impacted by anything, light waves or anything else.
I suspect that the verb impact meaning ‘impinge on’ survives as (or has developed as) a bit of jargon in discussions of vision, and that Amy came across it there, and mistakenly concluded that the verb impact was acceptable only there. (If Real Scientists say it, then it’s ok.)