The use of large corpora provides abundant evidence of the actual usage
of grammatical structures and function words and reveals the language
behaviour of native speakers. One of the principles of corpus linguistics
is that meaning is contextual: we can only identify the meaning of items
by investigating the contexts in which they occur. In this paper I use data
from a large corpus of English to describe the usage of three grammar
words: supposing (that), assuming (that), considering (that). By analysing
the regularities in the context of use of these grammar words I attempt
to describe their function in discourse and to reveal what one must
know in order to use and understand these words correctly. The results
show that supposing (that), assuming (that) and considering (that.) convey
different implications concerning the factuality of the clauses where they
occur.