If pressed to supplement Tweedledee's ostensive definition of logic with a discursive definition of the same subject, I would say that logic is the systematic study of the logical truths. Pressed further, I would say that a sentence is logically true if all sentences with its grammatical structure are true. Pressed further still, I would say to read this book.
Willard Van Orman QuineLife is agid, life is fulgid. Life is what the least of us make most of us feel the least of us make the most of. Life is a burgeoning, a quickening of the dim primordial urge in the murky wastes of time.
Willard Van Orman QuineOne man's antinomy is another man's falsidical paradox, give or take a couple of thousand years.
Willard Van Orman QuineI have been accused of denying consciousness but I am not conscious of having done so.
Willard Van Orman QuineAn indirect quotation we can usually expect to rate only as better or worse, more or less faithful, and we cannot even hope for astrict standard of more and less; what is involved is evaluation, relative to special purposes, of an essentially dramatic act.
Willard Van Orman QuineThe variables of quantification, 'something,' 'nothing,' 'everything,' range over our whole ontology, whatever it may be; and we are convicted of a particular ontological presupposition if, and only if, the alleged presuppositum has to be reckoned among the entities over which our variables range in order to render one of our affirmations true.
Willard Van Orman Quine