**Crab:** Ha! Frog doesn’t know what she’s talking about. She says that my knowledge of *waterology* is invalid because I don’t have a degree, and that she does. That’s *ad hominem* **and** *appeal to authority*. Clearly, the ocean is not changing, and she just proved it!

**Albatross:** Is that so? I don’t see how her dismissal of your argument proves anything about climate change.

**Crab:** Ah, my friend, let me introduce you to formal logic. *Modus tollens*, my friend. It states,

a -> b, !b => !a

*read: If a implies b, and b is false, then a is also false*

**Albatross:** I don’t see what that has to do with anything.

**Crab:** Look deeper, flappy fellow. *Modus Tollens*, in avian speak, means that if the argument is false, then the conclusion is false.

**Albatross squints. Crab isn’t sure if he’s confused his friend, or if the sun is in his eyes.**

**Albatross:** I don’t understand logic, but that doesn’t make sense to me. There are any number of arguments for and against any idea, and just because one of them is wrong, doesn’t mean the idea is wrong.

**Crab:** It’s logic! If the argument is wrong, the conclusion is wrong.

**Turtle:** Ahem. If I may.

**Crab:** Oh, bother. He’s such a bore.

**Turtle:** Logic is meaningless outside of tightly constrained rules and language. Words like ‘implication’ mean something different in logic compared to conversation.

**Crab:** That doesn’t have anything to do with anything. What’s your point? *Non Sequitor* - hah!

*Turtle glowers*

**Turtle:** No. Informal language and conversation - even the essays and books that you read - are too unconstrained for the hard rules of logic to make much sense. You’re mis-using logic and you’re being quite mean about it.

**Crab:** What’s that got to do with tides?

**Turtle:** You claimed that there is no change because Frog’s argument is invalid. I claim that you misunderstand logic, and hence have redefined and misused logic in communication. While your method of argument may be internally consistent according to your own rules, the rules of logic in argument are a model – and not universal. Therefore, you are not properly using logic – either your version, or formal propositional logic, in making or refuting a scientific argument about the tides.

**Crab:** What are you talking about? That’s exactly what logic is for, to make sure we state things in a clear, falsifiable manner. By the way, telling me that I do not understand logic is quite insulting, and that means-

**Turtle:** -you’re a foolish invertebrate. This sort of logic is best used in building and strengthening your own argument, and not in assessing the arguments and conclusions of others.

**Crab:* Nope. I learned logic as part of *critical thinking*. All I’m doing is thinking critically about the tide.

**Albatross:** I think I see what’s going on here. The rules of logic seem pretty abstract and complicated, but Crab is using them as if they are hard and fast rules for conversation.

**Turtle:** I agree. Logic, when used to examine an argument, does not usually prove anything. Instead, logic is better as a mechanism for illuminating and understanding ideas.

**Albatross:** If that’s the case, maybe logic is best used in ways where no one knows you are using it. For example, Crab could have learned from Frog’s approach that perhaps he does not provide evidence for his own points-

**Crab:** Again, I’m insulted! I’m no fool, and logic **is** my evidence.

**Turtle:** I’m hungry. I think I’ll see you two later.