Neither/Nor

@hales, Great question. The way you set up your diagram is fine, but G - ->not H and not Y combines both of those statements into one diagram, so it's easier to see what's going on. Your diagram and this one both mean the same thing, it's just that the one used in the explanation combines both rules so that they're easier to read and keep track of. Does this make sense? Let us know if you have any other questions!

I'm having trouble understanding the deduction the instructor makes from this rule. How would we know that G and H are not both from this rule?

@shafieiava, It is actually one of the rules of inference. neither H nor Y can be diagrammed as: ~ (H v Y) The rule of inference, known as De Morgan's Law, tells us that this statement is equivalent to: ~H & ~Y We can thus make an inference that: G -> ~(H v Y) is the same as: G -> ~ H & ~Y Even if you forget the rule, you could make the same inference using natural language. Neither..nor..always means that neither of these conditions could be true, or both must be false. For example: Dogs can neither read nor write. We understand this sentence to mean that dogs cannot read AND dogs cannot write. Both - can read and can write - must be false. Does that make sense? Let me know if you have any further questions.

When I wrote this rule, I wrote it as G-> not H or not Y but the instructor wrote it as G-> not H and not Y.... is "nor" considered "and" or "or"?