Produced by Charles Wells Revised 2014-12-27 Introduction to this website website TOC website index blog
The nature of proofs
The role of proofs in math
Presentation of proofs
Forms of proof
And, or, not
Universally true assertions
This is the top page of the chapter on Proofs.
Proofs cause problems to people new to abstract math:
A proof is an argument intended to persuade other mathematicians of the correctness of a statement. A proof has two main aspects: Its logical structure, and its presentation (the way it is written).
A proof has a precise logical structure:
The logical methods of deduction are described briefly in Mathematical reasoning. Some of the ways these methods are expressed in written proofs are described in Forms of Proof.
Most proofs at the college level or higher are written in narrative form, resembling an essay. To read such proofs you must learn how to extract the logical form of the proof from the narration. (This is called the translation problem.) To do this, you must be familiar with the conventions used to write narrative proofs and with the rules of logical deduction, since most simpler deduction rules are used without mentioning them. The articles Presentation of Proofs and Forms of Proof gives some examples of how narrative proofs work.
At the beginning of this article, I wrote:
To verify that a mathematical statement is correct, you must prove it. Evidence does not count in math. This section spells out in more detail what I mean.
The only way to verify that a claim about mathematics is correct is to prove it. Numerical evidence or the fact that the claim is true in some physical situation is suggestive but is not a verification.
See Evidence that fools you for some examples.
Mathematical proofs are public documents that can be challenged and defended using known principles. Any step in the proof can be challenged and a defender of the proof must analyze the step in more detail to show that it is correct - or to discover that in fact the step is incorrect and the proof is wrong!
This description of proofs shows how math is a part of science.
So the proof plays a role that is in some ways analogous to the role of experiments in other sciences. (This analogy should not be pushed to far, though.)
It is an observable fact that when mathematicians argue about whether some proposition is correct, they may argue heatedly for awhile but eventually the argument comes to an abrupt and total end: One party realizes that they have made a mistake, or both parties realize they had different definitions for one of the concepts they were arguing about.
Arguments among specialists in (say) literature or history are not like that - such arguments can and do go on for the lifetime of the participants.
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License.