THE study of speech-sounds has progressed more rapidly than other linguistic disciplines because its conditions admit of 'explanation'. The explanation results from the possibility of correlating the conclusions of two types of study, each assured of its own data. A historical study--phonology--gathers all the information available about a given speech-sound in isolation or in combination or as influenced in some way by others. A physical science--phonetics --tells us how this material is organized. The study is no less historical if the material to be explained is drawn only from the present, since 'now' is a moment in historical time. The investigator may pick any convenient moment in present or past time for a synchronic study designed to show how the elements of a given tongue are mutually related. As phonologist he gathers and sets out the facts, whether of modern English or ancient Greek; as phonetician, or with the help of a phonetician, he explains them. The explanation also is factual, and it may be urged that it does not go very deep nor tell us all we wish to know. It is both a source of satisfaction to the philologist, who finds he can treat with confidence of things of 2000 B.C., and of dissatisfaction to many others who feel that they have learned nothing essential concerning human speech. The latter includes operations of mind as well as of voice. But within their own limits both phonology and phonetics are positive sciences, and their interaction is such as to explain each other.
It has been of advantage to this branch of linguistics that psychological considerations rarely interfere. They play their part in the ordering of speech material, which is grammar, in preferences which constitute stylistics, and in the ramifications of vocabulary, but a sound as such is devoid of meaning. It is possible for sounds to gather associations, and to be deemed soft or harsh, musical or hissing, but such associations are inferred from use and wont; they are not inherent. Thus the phonologist gathers centum, cet, hund(red), ἑκατόν and šiMtas, sto, satǝm, çatam. He notes that often k is found in all Indo-European languages, but that in this series and all like it all like there is a systematic discrepancy. He posits, therefore, a