field of social science — they all follow the same method in their own domains.
The historian who discovers by whom Caesar was killed finds out that the new description "murderer of Caesar" can be applied to Brutus (and a few others) ; the linguist who follows up the etymology of a certain term discovers that a certain other word may be described as the "root of that term" and so forth.
Wherever there is a real progress of knowledge it always has the same character : it consists in giving a description of something in terms of something else, i. e. a description which is formed by a new combination of old signs.
Now it is time to remember what we had to say about language and Expression: it embodied the possibility of representing and communicating a fact by a new combination of old symbols. So we conclude: all genuine knowledge is Expression. This is, of course, not a mere coincidence, not just an interesting fact, but it constitutes the very essence of scientific as well as everyday knowledge.
This is of the utmost importance. I think we may say — and I hope you will be convinced of it at the end of the lecture — that all the misery of metaphysics is caused by the failure to see this point clearly. Knowledge is Expression; there is, consequently, no inexpressible knowledge. You cannot tell us: "Ah, I have discovered what this thing is, but it is impossible for me to say what it is". Real knowledge is recognition, so if you tell us that you really know a thing, you must be able to answer the question "Well, as what have you recognised it?"
Before drawing further conclusions from this insight we should find out whether there is a complete identity between knowledge and Expression by asking: if every knowledge is expression, is it also true that every expression is eo ipso knowledge ? In order to answer the question it is sufficient to consider expressions in our ordinary verbal language, in which everything else can be translated, that is to say, we restride ourselves to propositions in the usual form. Does every proposition convey knowledge?
We must immediately exclude mere tautological propositions which do not say anything and should perhaps not be regarded as propositions at all; we shall have to speak of them on a later occasion. After leaving
