We have now arrived at a stage in the formation of language where both _meaning_ and _meaningless_ words have been introduced, and where words have been made up out of combinations of the two. We see at once that with regard to meaningless words the use of them would naturally be fixed very much by tradition and custom; and whereas there might be a great many words standing for _ant_ and _hill_, and therefore a great many ways of saying ant-hill, for the meaningless words, such as _under_ and _on_, there would probably be only a few words. The reason of this is very plain. While all the separate synonyms for _hill_ expressed different ways in which it struck the mind, either as being high, or large, or steep, or what not, for _under_ and _on_, being meaningless words not producing any _picture_ in the mind, only one word apiece or one or two words could very well be in use. So long as _under_ and _on_ were significant words, meaning, perhaps, as we imagined, _head of_, or _foot of_, there would be plenty of synonyms for them; but only one or two out of all these would be handed down in their meaningless forms. And it is this very fact which, as we have seen, accounts for all the grammars of all languages, every one of those grammatical terminations which we know so well in Latin and Greek, and German, having been originally nothing else than meaningless words added on to modify the words which still retained their meaning. We saw before that it was much more natural for people to say ‘rock-on’ or ‘hand-in’ than ‘on the rock’ or ‘in the hand’--because rock and hand were the most important ideas and came first into the mind, while _on_, _in_, etc., were only subsidiary ideas depending upon the important ones. If we stop at rock or hand without adding _on_ and _in_, we have still got something definite upon which our thoughts can rest, but we could not possibly stop at _on_ and _in_ alone, and have any idea in our minds at all. It is plain enough therefore that, though we say ‘on the rock,’ we must have the _idea_ of all the three words in our mind before we begin the phrase, and therefore that our words do not follow the natural order of our ideas; whereas rock-on, hand-in, show the ideas just in the way they come into the mind.