This study is based on Geoffrey Leech’s claim that the frequency of modal auxiliary verbs has changed over a time span of 30 years (Leech 2002). In addition the diachronic development, Leech points to an interesting difference if we look at use of modal auxiliaries from a synchronic perspective. American English (AmE) tends to make far less use of these verbs than British English (BrE), and there is generally a sharper rate of decline in BrE.I am particularly interested in researching the nature of this reduction, and the extent to which corpus linguistics can be utilized in an investigation into ongoing linguistic change.A range of corpora were therefore selected in order to investigate the use of ought. The diachronic perspective was investigated using material ranging from that produced in the late 1950’s, to the most recent material which had been published in 2007. The synchronic perspective was also considered, mainly focusing on the American and British varieties of English, but also occasionally comparing these to New Zealand and Australian English. The use of ought in different genres was investigated quite thoroughly, and in connection with this, the differences between spoken and written English were considered. In addition to this, an attempt was made to discover how the word is being replaced by looking at the development in the use of possible replacement expressions.The findings from this investigation reveal that there is an ongoing reduction in the use of ought in American as well as British English. Perhaps unexpectedly, there is a tendency for ought to be more common in spoken than in written language. Another clear pattern is the tendency for ought to be increasingly restricted to formal language. The findings also seem to reveal a development where the use of ought in the sense of implying some kind of obligation is becoming increasingly dominant. This, coupled with the findings that there is a decline in the use of ought with second person subjects, and an increasing tendency for the “target” of an ought (to)-clause to be an inanimate third person may indicate that there has been a semantic shift when it comes to this particular modal auxiliary, and that its face threatening potential is increasing.When it comes to the use of corpus in this type of language research, I hope to have demonstrated how information regarding actual language in use may be accessed in this way, thus enabling researchers to observe and describe linguistic variety, both when it comes to diachronic development, and synchronic variation. I hope to have shown how a range of corpora may be used in order to investigate different aspects of language use, and reduce bias resulting from compilation methods. Thereby, I aim to prove that corpus research is a useful tool in a comparative study such as this, even in instances where he corpora which are used are not necessarily designed for this purpose.