In comparison with classifications of semantic change the problem of their causes appears neglected. Opinions on this point are scattered through a great number of linguistic works and have apparently never -been collected into anything complete. And yet a thorough understanding of the phenomena involved .in semantic change is impossible unless the whys and wherefores become known. This is of primary importance as it may lead eventually to a clearer, interpretation of language development. The vocabulary is the most flexible part of the language and it is precisely its semantic aspect that responds most readily to every change in the human activity in whatever sphere it may happen to take place.
The causes of semantic changes may be grouped under two main headings, linguistic and extralinguistic ones. Of these the first group has suffered much greater neglect in the past and it is not surprising therefore that far less is known of it than of the second. It deals with changes due to the constant interdependence of vocabulary units in language and speech, such as differentiation between synonyms, changes taking place in connection with ellipsis and with fixed contexts, changes resulting from ambiguity in certain contexts, and some other cases.
Semantic change due to the differentiation of synonyms is a gradual change observed in the course of language history, sometimes, but not necessarily, involving the semantic assimilation of loan words. Consider, for example, the words time and tide. They used to be synonyms. Then tide took on its more limited application to the periodically shifting waters, and time alone is used in the general sense.
Another example of semantic change involving synonymic differentiation is the word twist. In OE it was a noun, meaning 'a rope' whereas the verb thrawan (now throw) meant both 'hurl' and 'twist'. Since the appearance in the Middle English of the verb twisten ('twist') the first verb lost this meaning. But threw in its turn influenced the development of casten (cast), a Scandinavian borrowing. Its primary meaning 'hurl', 'throw' is now present only in some set expressions. Cast keeps its old meaning in such phrases as cast a glance, cast lots, cast smth. in one's teeth. Twist has very many meanings, the latest being 'to dance the twist'
Fixed context may be regarded as another linguistic factor in semantic change. Both factors are at work in the case of token. When brought into competition with the loan word sign, it became restricted in use to a number of set expressions such as love token, token of respect and so became specialized in meaning. Fixed context has this influence not only in phrases but in compound words as well. OE mete meant 'food', its descendant meat refers only to flesh food except in the set expression meat and drink and the compound sweetmeats.
No systematic treatment has so far been offered for the syntagmatic semantic changes depending on the context. But such cases do exist showing that investigation of the problem is important.
One of these is ellipsis. The qualifying words of a frequent phrase may be omitted: sale comes to be used for cut-price sale, propose for to propose marriage, to be expecting for to be expecting a baby. Or vice versa, the kernel word of the phrase may seem redundant: minerals for mineral waters. Due to ellipsis starve which originally meant 'die' (cf. Germ sterben) came to substitute the whole phrase die of hunger, and also began to mean 'suffer from lack of food' and even in colloquial use 'to feel hungry'. Moreover as there are many words with transitive and intransitive variants naming cause and result, starve came to mean 'to cause to perish with hunger'.
English has a great variety of these regular coincidences of different aspects, alongside with cause and result, we could consider the coincidence of subjective and objective, active and passive aspects especially frequent in adjectives. E.g. hateful means 'exciting hatred' and 'full of hatred'; curious—'strange' and 'inquisitive'; pitiful— 'exciting compassion' and 'compassionate'. Compare the different use of the words doubtful and healthy in the following: to be doubtful :: a doubtful advantage, to be healthy :: a healthy climate.
The extralinguistic causes are determined by the social nature of the language: they are observed in changes of meaning resulting from the development of the notion expressed and the thing named and by the appearance of new notions and things. In other words, extralinguistic causes of semantic change are connected with the development of the human mind as it moulds reality to conform with its needs.
Languages are powerfully affected by social, political, economic, cultural and technical change. The influence of those factors upon linguistic phenomena is studied by sociolinguistics. It shows that social factors can influence even structural features of linguistic units, terms of science, for instance, have a number of specific features as compared to words used in other spheres of human activity.
The word being a linguistic realization of notion, it changes with the progress of human consciousness. This process is reflected in the development of lexical meaning. As the human mind achieves an ever more exact understanding of the world of reality and the objective relationships that characterize it, the notions become more and more exact reflections of real things. The history of the social, economic and political life of people, the progress of culture and science bring about changes in notions and things influencing the semantic aspect of language. For instance, OE eorpe meant 'the ground under people's feet', 'the soil' and 'the world of man' as opposed to heaven that was supposed to be inhabited first by Gods and later on, with the spread of Christianity, by God, his saints and the souls of the dead. With the progress of science earth came to mean the third planet from the sun and the knowledge of it was constantly enriched.
