This article is an experiment to select `core expressions' in English for Japanese learners of the English language.  English sentences have traditionally been thought to be com-posed of phrase(s), and phrases are composed of word(s). This is partly true, but from this point of view, words are the basic elements to be learned and stored in our brain, which are later combined by grammatical rules. However, this 'word-based' theory seems to be wrong.  There seems to be many cases in English where the occurrence of one word predicts the occurrence of another, either following or preceding it. Many of them do not make `idioms' but they are very close combinations of highly used frequent words. These close combinations of words or collocations are reasonably stored in our brains as a unit. It is these collocations that greatly decide whether our expressions are natural or not although it is sometimes very difficult to explain why.  By examining all the texts in Japanese high school textbooks "English I and II", the author tried to find what combinations there are and then examine which should be included among essential collocations for the Japanese learners of English.