The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

Addition Facts

Date: Thu, 29 Jun 1995 00:23:23 +0300
From: Anonymous
Subject: adding 2 numbers


I'd like to understand the reason for the 'fact' that 2+2 = 4.
(It's not a joke, it really interests me to understand this.)

Date: 5 Jul 1995 10:15:17 -0400
From: Dr. Ethan
Subject: Re: adding 2 numbers

Well this problem is as much philosophical as it is mathematical.
The easiest (and somehow least satisfying) way to answer you is to say 
that it is definitional that 1+1 = 2 and that n + 1 = the next number bigger 
than n.

So 2+2 is 2+1+1, which is 3+1, which is 4.  The other way to think about it
is that + signifies the combining of two quantities, and the name for the
quantity that is the same size as 2 combined with itself is 4.

It really does come down to the "fact" that that is the definition.

If your question is more about why + was chosen to represent this combining
operation, write back and I will help you out.

Ethan Doctor On Call
Associated Topics:
Middle School Number Sense/About Numbers

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.