Is an Empty Set a Subset?
Date: 08/31/2001 at 12:01:58 From: anabelle Subject: Proof Hello Dr. Math, The empty set is a subset of all sets, right? What is the proof of the example: For any event W in the sample space S, what is the proof that the empty set is a subset of W? Thank you.
Date: 08/31/2001 at 12:58:04 From: Doctor Peterson Subject: Re: Proof Hi, Anabelle. A subset of a given set is simply any set, all of whose elements are contained in the other. Since the empty set has no elements, all of its elements are in any other set! It sounds weird, but that's the way logic works. To put it another way, a set A is NOT a subset of B if there is some element x of A that is not in B. Since the empty set has no elements that are not in your given set, we can't say it is NOT a subset. That means that it is. To select a subset, we must look at each member of the set and decide whether to keep it. If we say "yes" to every member, we have the set itself; if we say "no" to all of them, we have the empty set. We could choose to exclude these from the definition of subset, but it makes a lot of things easier if we include them. That way there are no special cases to deal with when we state theorems. Here is an answer from our archives that deals with this question: Empty Sets http://mathforum.org/dr.math/problems/hood8.15.97.html - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.