Many years ago, when I took Algebra I and Geometry, I had to learn the logic that goes with simple If-Then statements.
https://en.wikipedia.org/wiki/Contraposition:
If A, then B. If statement A is true, then statement B must also be true. For logic like this, True is defined as ALWAYS true, and False is defined as NOT always true. Let’s leave the abstract statements A & B and make this more specific. Let A = something is a cat, and B = it’s a mammal. It becomes: If it’s a cat, then it’s a mammal, a true Implication. If A is false (something is not a cat), the statement “it’s a mammal” is also false. The entire Implication would also be false.
If B is not true (not a mammal), then A must also be not true. This is called the Contrapositive of the original Implication. If an original Implication is true, then the Contrapositive must also be true – by definition. If the original Implication is false, the Contrapositive must also be false.
Here are all the various forms of If-Then statements, their Logic names, and their true/false status:
| Implication | If A, then B | If it’s a cat, then it’s a mammal | True |
| Contrapositive | If not B, then not A | If it’s NOT a mammal, then it’s NOT a cat | True |
| Converse | If not A, then not B | If it’s NOT a cat, then it’s NOT a mammal | False |
| Inverse | If B, then A | If it’s a mammal, then it’s a cat | False |
| Negation | If A, then not B | If it’s a cat, then it’s NOT a mammal | False |
Sometimes, if an original implication’s truth is not clear, it’s useful to look at the contrapositive. (I won't go into those other logic forms, Converse, Inverse, and Negation.)
Why am I going into any of this? Last Wednesday, Alan Dershowitz asserted in the Senate impeachment trial of Donald Trump, that “Every public official I know believes that his election is in the public interest. Therefore, if a president did something that he believes will help him get elected – something he believes is in the public interest – that cannot be the kind of
quid pro quo that results in impeachment.” I struggled to understand that.
Let’s apply some Logic 101.
If A (doing something he believes is in the public interest), then B (it cannot be impeachable).
Dershowitz claims this is a true statement. If so, the Contrapositive should also be true… If NOT B, then NOT A.
If something CAN result in impeachment, then the president DID NOT DO something that he believes would help him get elected – this would also be something AGAINST the public interest.
Huh? Something is clearly wrong here. If the original Implication is true, then the Contrapositive should also be true. Instead, it makes no sense at all. If anything, it sounds more irrational than his original Implication. To carry this one step further, the Contrapositive of his original Implication says:
Something that is against the public interest – losing an election or re-election – would be grounds for impeachment.
Why bother with an election or re-election if it’s unconstitutional to lose? Alan Dershowitz flunks Constitutional Law, must less Logic 101.
Dershowitz’s grew up in Brooklyn, where con-artists with a cocky attitude are a dime a dozen. Imagine Bugs Bunny. Bugs had that Brooklyn accent – and that classic Brooklyn attitude. Dershowitz may have spent some 50 years at Harvard Law School, but 50 years wasn’t long enough for him to loose ‘dat Brooklyn attitude’. Those skills may have contributed to his success as a court room defense attorney, but they fail at Constitutional Law.
If Dershowitz asks to you to make change for a $20 bill, just walk away. Never play poker with him – and never ever take him up on an offer to sell you a bridge.
