Quotes from Graham Priest

to know that an inference is deductively valid is to know that there are no situations in which the premisses are true and the conclusion is not.

if it was so, it might be; and if it were so, it would be: but as it isn't, it ain't. That's logic.

or refuting, with his guidance, a famous refutation of the existence of time, will be worth it.

This book is an introduction to logic, as contemporary logicians now understand the subject. It does not attempt to be a textbook, however.

I know what you are thinking about', said Tweedledum: 'but it isn't so, nohow.' 'Contrariwise,' continued Tweedledee, 'if it was so, it might be; and if it were so, it would be: but as it isn't, it ain't. That's logic.