Overarching Differences between Polite Form and Casual Form
Before rushing into learning formal Japanese (敬語・けいご), let’s look in the other direction a little bit. Formality and respect is something that is highly valued in Japanese society, but when talking to a school friend or a little sibling, it would seem like overkill to tack です/ますonto every sentence. This is where casual form fits in.
です/ますUsage: When casually speaking, you generally do not bother using the ます or polite form of verbs. Generally when indicating an action, you can use the plain or dictionary form while speaking.
For Example, say you want to say the sentence “Because I have a cold, I will go home early today.” In polite form, this could be said as:
かぜがひきましたから、今日早く帰ります。 かぜ が ひきました から、きょう はやく かえります。
In a more casual form, this could be said as:
かぜがひいたから、今日早く帰る。 かぜ が ひいた から、きょう はやく かえる。
Another important thing is the fact that です can sometimes be implied in a sentence, and doesn’t always have to be explicitly stated.
For Example, say I would like to ask my little sister what she wants to do this weekend. A more polite way to say this could be:
今週の週末に何がしたいですか。 こんしゅう の しゅうまつ に なに が したいですか。
And a more casual way to say this could be:
週末に何がしたい？ しゅうまつ に なに が したい？
In more casual speech, you can also imply the subject of the sentence without specifically saying this. If I’m discussing my likes and dislikes with a friend who asked me about them, there really is not a need to put “私は” in front of everything and can just say “＿がすきです” instead.
Adjective Usage: Some of the adjective endings can also be changed to seem a little less stiff or formal. ですcan sometimes be omitted when talking about いadjectives – so instead of “あの人は優しかったです” you can say “あの人は優しかった.” For なadjective phrases, there are some substitute endings you can use that will make the sentence seem more casual.
ですloosely can be swapped withだ
NOTE: This swap doesn’t work if ですis part of an interrogative- such as ですか!
でしたcan be swapped with だった
For example, すきでした can be すきだった – see the previous note
ではありません and じゃないcan be swapped
For example, すきではありませんandすきじゃない
ではありませんでした and じゃなかったcan be swapped
For example, すきではありませんでした and すきじゃなかった
Words that begin with お
In Japanese, there are many words in which you put "お" in front of, even though there's no need to. An example of this is the word お手伝い (おてつだい・otetsudai・help or chore), where you can just say 手伝い. Another would be the word お花(おはな・ohana・Flower) that could just be said as はな.These words are called 女房言葉 (にょうぼうことば・nyoubou kotoba・literally, "wife word"). They're words that women of high class started to use around the 14th century, and were seen as a polite way of saying things. Later they spread to general use where today, it’s used as a respectful prefix. They're mostly used for native Japanese nouns, but there are many exceptions, making it difficult to define a clear grammatical rule. This makes女房言葉one of those things that Japanese people use depending on whether it "sounds rights" or not. If you know words that can have a “お” prefix, it's safer to use those words since that is acceptable in both polite and colloquial Japanese (unless if your intention is to speak "gangster" like.) If you’re speaking in formal Japanese, you want to make sure you are using “お” when you should be using it.