It's more precise than "if": webbob's example of "You can crash at my place iff I'm home that weekend" wouldn't be that ambiguous as just "if", but the "only if" clarifies.
It's used a lot more in mathematics than in other contexts.
I don't think I've ever heard it in a context other than mathematical logic. It's not English.
And I don't think of it as more precise than "if"; I think of it as different. "And" isn't more precise than "or," even though the former subsumes the latter.
In mathematical writing, I encounter and write both. One might say "The Axiom of Choice is a necessary and sufficient condition for Zorn's Lemma," but when you're in the middle of an argument, it's much more convenient to have a simple conjunction that you can use as one would other logical connectors like "and" and "or".
No, precisely right it isn't. It's a logical operator, and the moment you invoke it, all the basic rules of logic, including the potentially annoying Modus Tollens, come along for the ride.
Do you feel that way about the other logical operators? (and, if, if not, etc) Some of them are useful in casual usage as well as strict construction.
I don't find the abbreviation "iff" useful in english. It's too easy to overlook that extra "f," or mistake it for a typo. If it's important to specify "and only if," it's worth 3 words to specify it properly and increase the chance it will be recognized and understood.
Do you feel that way about the other logical operators? (and, if, if not, etc) Some of them are useful in casual usage as well as strict construction.
Um. To some extent, yes. Depends on context. I'm most likely to be sent off into logic land by sentences of the form "If...then..." But just this morning I restrained myself from arguing with minnehahaB about whether 'and' subsumes 'or,' or whether, as I would be tempted to say wrt logic operators, that 'or' subsumes 'and' and the latter is in fact more precise than the former. See? There I go again.
But I agree with you that 'iff' isn't that handy for ordinary English usage; indeed, I'm tempted to say that even writing out "if and only if" isn't that handy, because it inevitably uncovers someone who doesn't understand double implication and then I'm all too tempted to get didactic about it.
It certainly is English, it's right here in my Merriam-Websters Tenth. In fact, it's a great trivia question to ask someone to name a five syllable word that is only three letters long. (Pronouncing it "if-fuh" is also permitted, but I think unusual because it sounds so much like "if" while having a very different meaning.)
It's a pity that "xor" isn't a word, because we need that too. "and/or" is an abomination.
The trouble is that English 'or' tends to lean toward exclusive 'or' in connotation. If it were the 'or' of logic, then you could just say 'or' for "and/or" and be done.
"Or" pulls double duty. Evidently, if you asked my college math professor "Would you like coffee or tea?", his respose would be "Yes, I would."
So if you're talking about a decision between a number of alternatives, then that is exclusive by understanding, I agree. But when you're talking about the connective between logical statements, it's not so clear to me. For example, consider "You should change the oil in your car every three months or three thousand miles." One would not conclude "I don't need to change my oil because it has been a year and eight thousand miles since the last time I changed it."
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It's more precise than "if":
It's used a lot more in mathematics than in other contexts.
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And I don't think of it as more precise than "if"; I think of it as different. "And" isn't more precise than "or," even though the former subsumes the latter.
B
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Which is the term I hear in philosophy.
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No, precisely right it isn't. It's a logical operator, and the moment you invoke it, all the basic rules of logic, including the potentially annoying Modus Tollens, come along for the ride.
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I don't find the abbreviation "iff" useful in english. It's too easy to overlook that extra "f," or mistake it for a typo. If it's important to specify "and only if," it's worth 3 words to specify it properly and increase the chance it will be recognized and understood.
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Um. To some extent, yes. Depends on context. I'm most likely to be sent off into logic land by sentences of the form "If...then..." But just this morning I restrained myself from arguing with
But I agree with you that 'iff' isn't that handy for ordinary English usage; indeed, I'm tempted to say that even writing out "if and only if" isn't that handy, because it inevitably uncovers someone who doesn't understand double implication and then I'm all too tempted to get didactic about it.
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It's a pity that "xor" isn't a word, because we need that too. "and/or" is an abomination.
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So if you're talking about a decision between a number of alternatives, then that is exclusive by understanding, I agree. But when you're talking about the connective between logical statements, it's not so clear to me. For example, consider "You should change the oil in your car every three months or three thousand miles." One would not conclude "I don't need to change my oil because it has been a year and eight thousand miles since the last time I changed it."
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Yes, I tend to be tediously predictable in this way, myself.