“The formal version of this would use します instead of する”
“Since you’re speaking casually, you don’t have to use です”
I see statements like this all the time, and it always makes me twitch a little bit. It’s a bit of an “all squares are rectangles” problem; certainly much casual speech is informal, and certainly much polite speech is also formal, but there’s more to the story than just these two cases. In fact, there are two pairs of opposite modes, which together produce four noteworthy combinations:
- Polite vs Non-polite
- Formal vs Colloquial
Let’s define each one of these modes before we move on to mixing them together.
The technical Japanese term for “polite speech” is 丁寧語, which simply refers to sentences which use the copula です and the ます auxiliary verb to encode words with a sense of respect for the other party’s boundaries. Using 丁寧語 with people you are unfamiliar with is common courtesy, and when used with superiors (regardless of familiarity) it signals that you are aware of your place in the social hierarchy.
It’s common to refer to 丁寧語 as 敬語, though I prefer not to do this as it is a slight oversimplification; again, 敬語 includes 丁寧語 but they are not equivalent.
The hallmark of non-polite speech is the use of plain-form verbs and the copula だ. Whereas polite speech signals a certain amount of respect for the other party, non-polite speech does not — however, this is not the same as saying that it signals a lack of respect. Rude speech, like the auxiliary verb やがる or abrasive pronouns like てめえ and お前, fall under this category, but it important to remember that not all non-polite speech is automatically rude.
Moving on to the second of our two pairs, formal speech is characterized by precision and correctness. When speaking formally, most contractions are off the table, as are slang words (or proper words which have come to take on alternative meanings). Formal speech is textbook Japanese; any terms used will be easily found in a dictionary, particles will rarely be omitted, and the grammar will be orthodox.
I’ve chosen to call this final mode “colloquial” rather than “informal” because this term comes with some additional nuance in English which I feel might muddy the waters. Colloquial Japanese speech includes short forms like the endlessly versatile って, contractions of の into ん, and terms like 元カノ, which would not be used in a “proper” setting. Colloquial language is always in flux and may appear somewhat impenetrable from an outside perspective.
Now that we’ve defined these four modes, let’s combine them into four different registers and give some examples of when each one would be used.
Polite / Formal
Many learners will be introduced to this register in the early days of their study, and most people will refer to it interchangeably as “polite” and “formal”. This is the standard in the workplace, even amongst peers in many cases (superiors may use non-polite/formal language to their subordinates), and is common in public-facing communication where no direct relationship exists; for example, instructions for the JLPT are given in non-敬語 polite/formal Japanese.
Polite / Colloquial
It may come as a surprise that two people can be on friendly terms and yet still use polite language with each other, but in actuality it’s very common. For example, in a 先輩 後輩 relationship, the 後輩 will always use polite language when speaking with her 先輩, but may still use various colloquial forms and terms. Consider something like 風邪引っちゃいました — it omits を particle and uses the てしまう contraction ちゃ, but still finishes with ました to encode the sentence with politeness.
Non-polite / Formal
Another potentially unexpected combination that has a huge corpus of examples: all of Japanese Wikipedia is written in non-polite / formal language. Again, we have a situation where the writing should be precise and orthodox in order to be easily understood, and also no particular 相手 relationship to be respectful of. This is also (in my experience) the standard register for novels; the major differences between books is that some will use the copular verb である rather than だ (these styles are known as である体 and だ体 respectively; the former being more literary and the latter being more “speech-like”).
Non-polite / Colloquial
The last register on our list is also known as タメ口; the casual, frank manner in which good friends in an equal relationship will use when hanging out together. Bear in mind there is still some nuance here; just because you can speak casually with a friend in some circumstances doesn’t mean it will always be appropriate. For example, coworkers might speak politely to each other at work but switch to タメ口 when they leave for the night; or childhood friends of different ages might use タメ口 normally, but switch into the polite/colloquial 先輩・後輩 dynamic when at school.
It should go without saying that these combinations are not exhaustive — each mode contains a spectrum, from abrasive to friendly to perfunctory to reverent. The social dynamic at large is not something that can be truly learned from any article, so I highly recommend that you get out there and form your own intuitive understanding by engaging with native media and speakers. In the meantime though, hopefully this has been a helpful introduction to some speech registers that often go overlooked.