CRITICAL THINKING – Fundamentals: Necessary and Sufficient Conditions [HD]

(intro music) Hi, I'm Kelley Schiffman! I'm a PhD student at Yale University. And today I want to talk about necessary [br]and sufficient conditions. We hear the words "necessary" and [br]"sufficient" all the time. "Merely taking the test isn't sufficient [br]for passing it." "The lawyer convinced the jury that there is sufficient evidence to [br]convict the accused." "Pain is a necessary part of every human[br]life." "Practice is really necessary for [br]success." But what exactly do these words mean? If P is necessary for Q, then Q cannot be[br]true unless P is true. Philosophers sometimes put this by saying[br]that Q is true only if P is true. Let's consider a case to helps us get [br]clear on this. What's necessary for getting accepted to [br]a university? Well, you might think that one necessary [br]condition is being human. You can only be accepted to a university[br]if you are human. Another necessary condition is submitting[br]an application. You can't get accepted to a university [br]unless you apply there. Another necessary condition is perhaps[br]having decent grades. Okay, so what about sufficient conditions? If p is sufficient for Q, then P's being [br]true is enough to make Q true. Philosophers often put this by saying that[br]if P is true, then Q is true. Now it's a little harder to think of a [br]sufficient condition for getting accepted to a university. But consider some seventeen year old who[br]just won the Nobel Prize in chemistry. Seems like that is pretty sufficient for [br]getting accepted to university. Now, necessary and sufficient conditions [br]come in all combinations. Here is an example of a necessary, but [br]not sufficient, condition. Steering well is a necessary condition[br]for driving well. You can't drive well unless you steer [br]your car well. However, steering well is not sufficient [br]for driving well, since steering well is not enough to make[br]it true that you are driving well. You could steer well but still drive badly[br]for other reasons. Here is an example of a sufficient but [br]not necessary condition. Boiling potatoes in water is a sufficient[br]condition for cooking them, since it's true that boiling potatoes is [br]enough to cook them. However, boiling potatoes in water is not [br]a necessary condition for cooking them, since you can cook them in many other [br]ways: frying them, grilling them, baking them, [br]roasting them. And finally here is an example of a [br]necessary and sufficient condition: getting all of the answers correct on a [br]test is necessary for getting a perfect score[br]on the test, because you will not get a perfect score [br]on the test unless you get all the answers correct. Getting all of the answers correct is also[br]a sufficient condition for getting[br]a perfect score, because getting all of the answers correct[br]is enough to get a perfect score. There is nothing else you must do in order[br]to get a perfect score. Subtitles by the community

29 thoughts on “CRITICAL THINKING – Fundamentals: Necessary and Sufficient Conditions [HD]”

  1. Here are examples for a conditions which are neither necessary nor sufficient:

    Having a diesel engine in a car is neither necessary nor sufficient for the car to work.

    If you have to correctly answer 70 out of 100 questions for passing a test, it is neither necessary nor sufficient to correctly answer question 5. (Or any other particular question)

  2. and what if your exam paper get lost? then you wont take that perfect score…do we assume things like this or not?

  3. lets assume that i want to go from germany to france..if i take flight is sufficient condition to get there? i mean maybe the plane drops it doesnt guarantee this even if i go with car or train mb something broke during the trip..but i think that we dont assume this i wrong? thx in advandance

  4. This is great. I learned logic in a discrete math class but when "p implies q" got replaced with a "necessary" or "sufficient" statement, I couldn't remember which one was which.

  5. To avoid getting screamed at by my wife, I have to not screw up in any way; I have to put everything in its right place, not forget any little detail, make sure the tiniest little detail is perfectly sorted out. Getting everything 100% perfect is necessary to avoid a roasting. Unfortunately, however, it is by no means sufficient.

  6. Just wanna make sure:
    If p is sufficient for q, then we can say "If p, then q"
    If p is necessary for q, we can say say "If not p, then not q"

    If p is both necessary and sufficient for q, do we say "If and only if p, then q"?

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