There is also the question of the opposite phenomenon — that of nouns becoming adjectives. For a variety of reasons, this question presents a number of difficulties and has, accordingly, given rise to prolonged and inconclusive discussions. The facts are, briefly stated, these. In Modern English a noun may stand before another noun and modify it. Witness numerous formations of the type stone wall, speech sound, peace talks, steel works, the Rome treaty, etc. The question, as usually asked, is, whether the first component of such phrases is a noun or whether it has been adjectivised, i. e. become an adjective. 1 Different views have been put forward here. The view that the first element of such phrases as stone wall is a noun has been defended by H. Sweet 2 and others, the view that it is an adjective or at least approaches the adjective state, by O. Jespersen 3 and others, and finally the view has also been expressed that this element is neither a noun nor an adjective but a separate part of speech, viz. an attributive noun. 4 The very variety of opinions on the subject shows that the problem is one of considerable difficulty. We shall become aware of that peculiar difficulty if we attempt to apply here the criteria serving to distinguish a noun from an adjective. It must be stated at once, though, that one criterion, namely that of degrees of comparison, is useless here. The first element of those phrases is indeed unable to form degrees of comparison, but that in itself does not prove that the element is not an adjective, since many adjectives, e. g. wooden, woollen, European, do not form degrees of comparison either. The criteria to be applied here are the following: (1) Has the first element of those phrases number distinctions? (2) Is it able in the cases when it denotes a human being to have a possessive form? (3) Does it denote a substance or a property? Strangely enough all these questions are very hard to answer. As to (1), it must be stated that the first element usually appears only in one number form, which is either singular or plural, e. g. stone wall, not stones wall; house fronts, not houses fronts; goods van, not good van, etc. However, that observation leads us nowhere. It is quite possible to argue that the first element is a noun, capable of number distinctions, but always appearing in a definite number form when making part of that phrase. So the application of criterion (1) proves to be inconclusive. As to criterion (2), we also run into difficulties. If, for example, we take the phrase the Einstein theory and ask whether the first element can take the possessive form, we shall have to concede that of course it can; thus the phrase Einstein's theory is quite possible, and indeed, it occurs in actual texts. However, those who hold that it is not a noun, but either an adjective or an attributive noun (meaning a special part of speech) argue that the word in the phrase the Einstein theory is not the same word as in the phrase Einstein's theory and that the word in the first of these groups is incapable of taking a possessive form. Thus, it appears to be impossible to come to a definite conclusion on the basis of this criterion. Now we proceed to criterion (3). How are we to decide whether the word Einstein in the former group denotes a substance or a property? There seems to be no perfectly convincing argument either way. We might say that it denotes a substance but this substance only serves to characterise the property of the thing denoted by the noun. Thus, we reach the conclusion that no perfectly objective result can be attained in trying to determine what part of speech the first element in such phrases is. This explains the existing difference of views on the subject and we are compelled to recognise that the question can only be solved in a somewhat subjective way, according as we start from one premise or another. If we start from the premise that we shall not speak of homonyms, or indeed new parts of speech, unless this is made strictly necessary by indisputable facts, we will stick to the view that the first element of such phrases as stone watt or speech sound is a noun in a special syntactical function. It is this view that appears to be the most plausible