This is Everyday Grammar, and today is a large day. No, that doesn't quite sound right. I mean a big day. In English, we use the phrase big day, but not large day.
But why? The answer is collocations, and that's the subject of today's program. A collocation is a group of two or more words that is almost always used together. Here are a few more examples.
Heavy rain. Major decision. Break a habit. And make a mistake.
It would sound strange if someone said huge rain, leading decision, discontinue a habit, or do a mistake. Many people might understand the meaning, but {native English speakers|英語ネイティブ話者|/ˈneɪtɪv ˈɪŋɡlɪʃ ˈspiːkərz/|Native English speakers use natural collocations.} would not combine words in this way.
Like in many languages, some words just go together in English, and some don't. There is no grammatical reason. So knowing that major decision is a collocation, for example, is not something you could easily guess.
And some English words can have many collocations. For instance, decision can also be used in big decision, difficult decision, final decision, and others. Learning your use of collocations will help your English sound more natural, which will