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When saying "Someone can A if B", does it imply "If someone does not B, someone cannot A"? So if I want to say "B is an option for A, but B is not necessary to achieve A", is "Someone may A if B" closer to this? Or is "Someone can A if B" good enough for this meaning?

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Without a lot more context, this is not a real question. –  FumbleFingers Mar 30 '12 at 23:56
    
As you can see from the various answers, it does not imply that at all, except when it absolutely does. Context is king. Without context, any guess is as good as any other, and any answer is more wrong (and more right) than the next. So in its current form the question is too broad and too vague, and we are closing it as such. We can reopen it, if you turn it into something specific and actually answerable. –  RegDwigнt Mar 31 '12 at 10:34
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closed as not a real question by FumbleFingers, Will Hunting, J.R., Matt Эллен, RegDwigнt Mar 31 '12 at 10:31

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

3 Answers

If I take your meaning, let's use the following example:

You can have ice cream if you finish your peas.

where A = ice cream and B = peas.

Regarding your first question:

When saying "Someone can A if B", does it imply "If someone does not B, someone cannot A"?

Yes.

Regarding your second question:

So if I want to say "B is an option for A, but B is not necessary to achieve A", is "Someone may A if B" closer to this?

May implies that a permission is being granted. In order to express that B is not necessary to achieve A, you could say something like:

  • Someone may A whether or not they have B.
  • B is not a prerequisite for A.
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No. For example:

Someone can fly if they have a plane. Clearly you can also fly if you buy a ticket on an airline or get someone else to fly you.

You can have a cheeseburger for lunch if you get here before noon. This clearly offers one way you can have a cheeseburger and doesn't imply you can't have a cheeseburger some other way even if you don't get there.

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Logically, "Someone can A if B" does not imply "If not B, then not A". The relevant concerns are necessary and sufficient conditions:

A necessary condition of a statement must be satisfied for the statement to be true.
A sufficient condition is one that, if satisfied, assures the statement's truth.

In your first example, "Someone can A if B" says B is sufficient for A; it does not say that B is necessary for A. There might be other conditions besides B that make A possible.

If you want to say "B is an option [that ensures] A, but B is not necessary to achieve A" with some precision, then perhaps say "B is sufficient but not necessary for A."

Saying "B is an option for A" is not quite right, because it does not mean "B is sufficient for A" but instead connotes that if you choose A, then B is available as an option.

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Right, 'can' implies necessary and sufficient as opposed to this: [if and only if](xkcd.com/1033 ) –  Jim Mar 31 '12 at 1:56
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