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Biconditionality, Contingency,
Necessity, Sufficiency
Or: Being very precise about
conditions for things
Today’s aim (s)
• To teach you some key terminology:
necessity, sufficiency, contingency, iff.
• To begin to think about d...
The Biconditional If(f)
• Sometimes the word ‘if’ only conveys a loose connection
between statements: “I will come with yo...
If or Iff?
1. I will die if I stop breathing
2. I can make a hot cup of tea if I have hot
water
3. I will pass my exams if...
Sufficiency,Contingency,Necessity
Take the example of the
statement, “I will grow up to
be very fit if I exercise and
eat ...
Contingency, Sufficiency, Necessity
• If you can be very fit without a good diet and
plenty of exercise, then these condit...
Why bother?
• Because for philosophers interested in analysing a
concept, only an exhaustive list of conditions for that
c...
To sum up
• A condition is necessary when it must be the case for
something to be true. But other conditions could be
need...
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What is knowlege 2016 revision biconditionality, contingency, necessity, sufficiency

  1. 1. Biconditionality, Contingency, Necessity, Sufficiency Or: Being very precise about conditions for things
  2. 2. Today’s aim (s) • To teach you some key terminology: necessity, sufficiency, contingency, iff. • To begin to think about definitions of belief, truth, justification and knowledge.
  3. 3. The Biconditional If(f) • Sometimes the word ‘if’ only conveys a loose connection between statements: “I will come with you to the pictures if you go on Friday”. But I could go with you to the pictures on another day. • However, if I say, “I will come with you to the pictures if, and only if, you go on Friday”, I am excluding other possibilities (such as going on Tuesday). • Philosophers call this if the ‘Biconditional If’ and spell it ‘iff’. Using ‘iff’ allows philosophers to specify conditions for things more precisely.
  4. 4. If or Iff? 1. I will die if I stop breathing 2. I can make a hot cup of tea if I have hot water 3. I will pass my exams if there is a miracle 4. If I eat any more I will be sick
  5. 5. Sufficiency,Contingency,Necessity Take the example of the statement, “I will grow up to be very fit if I exercise and eat sensibly”. • Might it be possible to be very fit without eating sensibly and exercising? • Are diet and exercise the only things that have a bearing on fitness?
  6. 6. Contingency, Sufficiency, Necessity • If you can be very fit without a good diet and plenty of exercise, then these conditions simply aren’t necessary. They are contingent. • But if, amongst other conditions, I must follow a good diet and take exercise to be healthy, then these conditions would be necessary. • And if diet and exercise were the only conditions that had to be met, then these conditions would be sufficient.
  7. 7. Why bother? • Because for philosophers interested in analysing a concept, only an exhaustive list of conditions for that concept to exist is good enough. • Philosophers like lists of conditions that are ‘individually necessary and jointly sufficient’. Because then these lists are really precise. • Necessity (needed, but not enough for) isn’t the same as sufficiency (the only thing(s) you need). • It is usually easy to think of necessary conditions. But very hard to think of sufficient ones. Try: defining what conditions must obtain for your smartphone to play music to your ears.
  8. 8. To sum up • A condition is necessary when it must be the case for something to be true. But other conditions could be needed too. • A condition or set of conditions is sufficient when only those things and nothing else must occur for something to be true. • Precisely specifying conditions allows for precise definitions. • It can be very hard to specify sufficient sets of conditions.

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