質問: In Genki I, になります and になりました are used interchangeably. Does になります imply "has become" and the other imply "had become"? For example, 1. 夏は暑くなります。 → (This) summer has become hot 2. 去年の夏は暑くなりました。→ Last summer had become hot Also, is it natural to use になっている for "is becoming"? Edit: This grammar is very short section in chapter 10 (section 5)
回答: 暑くなります refers to a general fact (if you are talking about what the summer in a certain country is like), or something in the future (if you are talking about one specific upcoming summer). 暑くなりました refers to something in the past. That said, なりました ("became") refers to a state **change** in the past, so you can say 暑くなりました in the middle of the summer while it's still hot. On the other hand, you cannot say 今年の夏は暑かった in the middle of the summer because this past tense implies it is no longer hot now.