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Comment by chrisweekly | Hacker News Reader

+1 for "iff" (if and only if), which I wish were more broadly used and recognized in written English

Except it's not used correctly here. "A iff B" means "A implies B and B implies A".

"I'd be willing to entertain, or even support, this way of them making money iff they spelled out honestly what they're doing and why" implies both of these:

- "If they spelled out honestly what they're doing and why, I'd be willing to entertain [...]"

- "If I'd be willing to entertain [..] then they will honestly spell what they're doing and why".

The second of which doesn't make sense to me, unless I'm missing something? He should have used "only if" rather than "iff" here.

I do think the second implication makes sense, if you take out the tenses, i.e.:

If I am willing to entertain then they honestly spell what they're doing and why.

It means that if you know that I am entertaining the idea you can infer from that they were honest.

I think the 'if' is the first point you list, and the 'only if' is saying that if Mozilla doesn't spell it out honestly then they'd not be willing to entertain which is a bit strange but logically equivalent to the second point you have.

Implication is not causation. "If I'd be willing to entertain [...] then they will honestly spell what they're doing and why", as if they wouldn't honestly spell it, there's no way I'd be willing to entertain the idea.

I believe the bidirectional implication in iff is logical implication, not causal implication. If the GP is willing to entertain ... then you can conclude Mozilla will honestly spell what they're doing. Iff in general use does not introduce a causal relationship, just a bidirectional set of conclusions. In other words, iff sets up necessary and sufficient conditions.

A iff B doesn't mean that B is because of A. It simply means that if A is true then B must be as well.

> - "If I'd be willing to entertain [..] then they will honestly spell what they're doing and why".

This is true, because if they won't, then you wouldn't be willing to entertain [..]

You're right, I guess it depends on what you choose A and B to be. For:

A = OP supports Mozilla making money from address bar ads

B = Mozilla is honest about making money from address bar ads

"B -> A" (OP supports Mozilla if Mozilla acts a certain way) makes sense. "A -> B" sounds confusing in a sentence, but its contrapositive, "!B -> !A", also makes sense.

However, for:

B = Mozilla decides to make money from address bar ads and is honest about reasons

"A -> B" no longer makes sense, since OP can support Mozilla having the address bar ads with an honest justification, but Mozilla can still decide to not have the address bar ads.

(1) IFF is shorthand for "if and only if". Try to read the original sentence, it makes perfect sense and is used correctly.

(2) Logically, iff, equivalence and double implication are themselves equivalent, the expression in question is (necessarily) logically correct even in those forms, though it is irrelevant as of (1) and a confusing way to express the relationship, as the causality clearly flows in one direction.

(3) It was not meant nor interpreted as a bare logical proposition, hence it is improper to blindly apply logical transformations and reinterpret in a different system.

I agree with all the other responses here that it is used correctly. First off, they are using it informally, and it's perfectly clear what they are trying to say, so even if it was formally wrong, exercises like these would still be tedious and beside the point.

But even playing the game of treating informal language by the rules of strict logical formalisms, it still makes sense. The two elements implying one another would be (1) trusting mozilla and entertaining this new program, and (2) mozilla communicating clearly about their ads. You trust them if they communicate honestly, and communicating honestly garners trust. Makes sense to me.

the fact that my first instinct was to mock you with "ummm ahhhctuallly" is telling that maybe your comment wasn't really needed.

We understand the intent and thought behind the use of iff in the original comment, regardless of what it may be interpreted to mean outside of a _very informal_ setting.

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