This is IV volume of eight in a series on Philosophy of the Mind and Language. For nearly a century mathematicians and logicians have been striving hard to make logic an exact science. But a book on logic must contain, in addition to the formulae, an expository context which, with the assistance of the words of ordinary language, explains the formulae and the relations between them; and this context often leaves much to be desired in the matter of clarity and exactitude. Originally published in 1937, the purpose of the present work is to give a systematic exposition of such a method, namely, of the method of " logical syntax".