Hi all,(adsbygoogle = window.adsbygoogle || []).push({});

I've got a question about indirect proof, whether I have understood it correctly:

a) Suppose I want to show A=>B, where A and B are two statements.

In the method of indirect proof I assume that [tex]\neg B[/tex] (not B) is true and use the given statement A to show a contradiction. Therefore, B must be true (because either B or [tex]\neg B[/tex] is true).

In short what I do:

[tex]\neg B[/tex] true (assumption) and A true (given statement) => contradiction

Is that correct?

b) Now another question:

Suppose I assume B is true (instead of [tex]\neg B[/tex] true) and use the given statement A such that it leads to a true statement like 1=1.

Have I showed anything with that?

In short what I do here:

B true (assumption) and A true (given statement) => no contradiction.

But that doesn't tell me anything, right?

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Indirect Proof (Logic question)

Loading...

Similar Threads - Indirect Proof Logic | Date |
---|---|

I An easy proof of Gödel's first incompleteness theorem? | Mar 6, 2018 |

A Indirect effect and spuriousity | Nov 17, 2017 |

Restore indirect relations within a transitive relation | Feb 25, 2014 |

Help with indirect logic proof please! | Mar 28, 2012 |

Determining Validity of Argument Using Indirect Truth Table | Dec 30, 2010 |

**Physics Forums - The Fusion of Science and Community**