Japanese is a verb-last language, and the types/forms of verbs and their modifiers that come at the end of the sentence will usually decide the speech level.
The below are all “I think so” at different speech levels. They are all verbatim, and don’t include analogous sentences like “I am of the opinion of”:
- 俺はそう思うよ -> Casual male
- 私はそう思うわ -> Casual female
- 私はそう思う -> Neutral
- 私はそう思います -> Polite or literary
- 私はそう思いますよ -> Polite and colloquial
- 私はそうと存じます -> Humble
- 私はそう思慮致します -> Very polite and literary
As you can see, the uses of ending particles (終助詞) like ”よ” and ”わ”, auxiliary verbs like “ます”, ”致します [致す+ます]”, a verb like “思慮する” change the speech level. You also see that different pronouns for “I” are used.
- For the use of pronouns, refer to the articles on “I“, “you“, “he/she/they“.
- For the use of gendered languages, refer to the article here.
The below are all “hurry up” at different speech levels.
- 早くしろ -> Male. Pretty rude
- 早くしてよ -> Casual male or female
- 早くして下さい -> Moderately polite
- 早くして頂けますか -> Pretty polite
Again you see the uses of ending particles (終助詞) like ”よ”, auxiliary verbs (助動詞) like “下さる”, “頂く” change the speech level.