What is the difference between necessary and sufficient?

@neologist,

Wood and a lighter are sufficient to start a fire but not necessary. You can use coal also. Oxygen on the other hand is necessary.

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I suppose Fresco would reason this is open for social "negotiation". It should depend on the majorities opinion ! Laughing

PS - It suffices to say I am more sceptic on "negotiation" effectiveness....

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@neologist,

I certainly agree with what Fil just said (in both posts)...but your question really needs (!) to be fleshed out a bit.

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@neologist,

These are two words usually conjoined as an adjective defining a quantity of something . Its like "high and Dry",

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@Fil Albuquerque,

Ordinary chemical reactions, yes. But magnesium will burn like hell in an atmosphere of pure nitrogen.

Point well made, though.

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Let's say someone throws a rock through your window. You suspect Snotty, the kid next door.

If you wish to prove your case, it would be necessary, but not sufficient to place him at the scene of the crime at the time.

For him to defend himself, it would be sufficient, but not necessary for him to prove he was in Boston.

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@neologist,

thats acceptable but, like my use, its not a unique phrase interpretation.

"Necessary" defines the qualitative attributes needed to establish something. Then, "Sufficient" quantifies how much of that attribute is needed to establish something completely .

Whats yer point anyway?
Are you still on that fossil fish thing?

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@neologist,

You got it wrong...in layman's terms "necessary" means fundamental, irreplaceable, while "sufficient" means enough but replaceable...
(...the use is not exclusive to Philosophy circles as farmerman in his infinite blissed ignorance suspects...he ought to give a shot at Law school for examples or any other area that requires Logic.)

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If I understand the underlying question implied by the OP, this may be related: http://plato.stanford.edu/entries/aristotle-causality/

Quote:

In Physics II 3 and Metaphysics V 2, Aristotle offers his general account of the four causes. This account is general in the sense that it applies to everything that requires an explanation, including artistic production and human action. Here Aristotle recognizes four types of things that can be given in answer to a why-question:

The material cause: “that out of which”, e.g., the bronze of a statue.
The formal cause: “the form”, “the account of what-it-is-to-be”, e.g., the shape of a statue.
The efficient cause: “the primary source of the change or rest”, e.g., the artisan, the art of bronze-casting the statue, the man who gives advice, the father of the child.
The final cause: “the end, that for the sake of which a thing is done”, e.g., health is the end of walking, losing weight, purging, drugs, and surgical tools.

If not, mea culpa.

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...1+1, 3-1. 5-3 are all sufficient for a 2 result. None in particular is specifically necessary for a 2 result.
Maths at work is necessary for accounting operations.

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Walking is sufficient to get to the restaurant, taking a cab also.
Moving is necessary to get there !

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Death of the victim is a necessary condition for a murder. Using a gun or a knife are just sufficient means to get it done.

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The underlying principle should be sufficiently clear by now, although is not necessarily understood. Basic brain power is fundamental.

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@neologist,

neologist wrote:

Your answer, please.

Boy oh boy, this thread is awash with bullshit already, from both respondents and OP alike...it's like no one, including the OP, actually understands the question.

Both terms are logical qualifiers/categories, not existential descriptors...it's embarrassing how ill equipped most of the interlocutors in this thread are to handle both that particular distinction and its appropriate context.

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You wont find any humans who know the difference between necessary and sufficient, if you could the planet wouldn't be in such bad shape .

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@Razzleg,

Are you being deliberately abstruse ? "Existential descriptors" ??? WTF are you talking about ?

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If Y is true only when X is true the X is a NECESSARY condition for Y !
Hope that helps Razzy boy !

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Necessity and Suficiency

Quote:

In logic, necessity and sufficiency are implicational relationships between statements. The assertion that one statement is a necessary and sufficient condition of another means that the former statement is true if and only if the latter is true. That is, the two statements must be either simultaneously true or simultaneously false. In ordinary English, 'necessary' and 'sufficient' indicate relations between conditions or states of affairs, not statements. Being a male sibling is a necessary and sufficient condition for being a brother. Fred's being a male sibling is necessary and sufficient for the truth of the statement that Fred is a brother.

Link: http://en.wikipedia.org/wiki/Necessity_and_sufficiency

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@neologist,

In everyday terms necessity and sufficiency are linked to the concept of "causality" which Hume showed was problematic.
e.g.
In cognitive science the modern view is that "the brain" is necessary for "cognition" but insufficient to account for it.
In biology heart failure is sufficient to account for death but not necessarily the main cause of it.
Note that both of these assertions may be subject to negotiation.

Context tends to govern semantics. A square (mathematically) necessarily has four equal sides, but a square (in town planning) need not. Contexts assume agreement about terms. Problems arise say when a theist proposes "God" as necessary for "existence" and an atheist claims that this is a vacuous tautology mimicking a mathematical definition.

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What is the difference between necessary and sufficient?

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