This post was prompted by a course of History of English langage.
It is only with this last, the Germanic group, that we are here concerned. But what is that makes this Germanic, and therefore English, Indo-European?
Indo-European is but one of a number of families into which the world's languages may be divided; and it must be remembered too that there are still many languages, and even whole groups, that have not been examined scientifically or committed to writing yet, and hence cannot be fitted into any scheme of classification.
Broadly speaking, it may be said that two outstanding characteristics indicate the Indo-Europeanness of a language; its structure and its vocabulary. Indo-European languages generally lend themselves in structure, at least if one knows something of their historical development, to that description of forms invented by the ancient Greeks and named by them "parts of speech".
A language may have inflexions fully retained relatively from the original Indo-European, like Russian, or it may have lost most of its distinctive word-endings like modern English: it may, as the grammarians say, be 'synthetic' with full inflexions or 'analytic' with few or none. But if we can think of its forms fairly readily as nouns, verbs, etc., that is to say under the traditional classical terms of 'Parts of Speech' it will probably be found to be Indo-European. Chinese, with its forms consisting not of parts of speech, but of what seem now to be merely monosyllabic roots, is therefore not Indo-European.
Or again, even in Europe, there are what are called 'Finno-Ugrian' or 'Uralian' languages - Hungarian and Finnish for instance, which do not show parts of speech, or even words in our ordinary sense always. Here a kind of phrase-complex takes the place of a clause or group of words and all kinds of things may be said about an object by building up a single root with prefixes and suffixes.
These languages are sometimes classified as 'agglutinative' or 'incorporating'. Many of the languages of Central Asia now in the former USSR are of this kind, and Kazak is one of them.
Germanic, then, is Indo-European in the sense that it uses parts of speech, whether with full inflexions synthetically as in its ancient forms, or with reduced inflexions tending towards the analytic, as in modern Dutch or English, and because it shares a fundamental nucleus of the vocabulary of the commonest things with other Indo-European tongues.