In Japanese sentences where reasons and causes are being expressed, you’ll find sentences that end in ですから (desukara) and からです (karadesu). Although they mean the same thing, there are two situations which distinguish the use of one from the other.
ですから (desukara) connects a subordinate clause to a main clause and functions like “because”. からです (karadesu) functions like “it’s because” and is used in question and answer situations where the main clause is already known from the context and is not stated. Both are used to express a reason.
First, let’s quickly review what から (kara) means and how it is used. A Dictionary of Basic Japanese Grammar tells us “…kara represents a reason or a cause. Thus, S1 kara S2 corresponds to ‘S2 because / since S1’”. In this definition, S1 ends with kara and states the reason or cause for a situation. S2 states the situation. Let’s have a look at an example.
健康にいいから、 毎日運動します。 Because it is good for my health, I exercise everyday.
In S1, what precedes から (kara) is usually in plain form, although it could also be in polite form in formal situations. S2 can be either in the plain or polite form depending on the situation. In the above example, から (kara) is placed in the middle of the sentences S1 and S2. Now let’s look at what happens when we switch the positions of S1 and S2 and から (kara) comes at the end.
Ending a Sentence with ですから (desukara)
毎日運動します。健康にいいですから。 I exercise everyday. Because it is good for my health.
Here, we see that the ending is ですから (desukara), and it’s the から (kara) that comes right at the very end. The definition from Genki tells us that “A sentence that ends with から (because) explains the reason or cause of a situation, a proposal and so forth.” The full two-sentence structure is “(situation)。 (explanation) から。” This definition corresponds to one given above, but the order of the information being stated is inverted. In both cases, we see から (kara) functioning as “because”.
One interesting to note is that when the order of the statement is “(reason) から、 (situation)”, the statement is one sentence with a comma after から (kara). Whereas when the order is “(situation)。 Reason から。”, the statement is broken into two sentences separated by a period.
In addition to です (desu) before から (kara), the above structure also works with ～ます (~masu) form verbs. Let’s have a look at an example.
日本語が少しずつ上手になってきます。毎日勉強していますから。 My Japanese is improving little by little. Because I am studying every day.
Ending a Sentence with (karadesu) からです
Now let’s take a closer look at sentences that end with からです (karadesu). Here it’s the です (desu) that comes right at the very end. Again, this pattern is used when the main clause is not stated because it is already known from the context, which is especially the case in question and answer situations. An example is below.
質: どうして今日はとても眠そうですか？ Q: Why do you seem so sleepy today? 答: 昨日の夜、よく眠らなかったからです。 A: It’s because I did not sleep well last night.
In this example, because the main clause was already known from the question, the answer did not need to restate it. Instead, it was replaced just with です (it’s). The combination of から+です functions as “it’s because”. But if desired, it is also possible to restate the main clause. It just makes the answer more verbose. See below.
答: 昨日の夜、よく眠らなかったから、今日はとても眠いです。 A: Because I did not sleep well last night, I am very sleepy today.
Another important point to note with this structure is that the verb, adjective, or noun that precedes からです (karadesu) is in the plain form. You wouldn’t use the polite form because the sentence already ends with です (desu) which is a polite form. Above was an example with the verb 眠る (to sleep), below is example with the な-adjective 好きな (liking).
質: どうしてあの人はあんなに知識豊富ですか？ Q: Why is that person so knowledgeable? 答: 図鑑を読むのが好きだからです。 A: It’s because they like to read the encyclopedia.
At this point, we have seen that there are two situations which distinguish the use of ですから (desukara) and からです (karadesu), but you will probably encounter cases in casual conversation when the answer to a question can be ですから (desukara). Don’t let this be confusing. In these cases, the full answer to the question was supposed to be of the form S1 kara S2, but the speaker just omitted saying S2 (the situation). Let’s compare the subtly different answers to the following question.
質: どうして最近毎日雨が降っているでしょうか？ Q: I wonder why recently it has been raining every day? 答1: 日本の梅雨からです。 A1: It’s because it’s rainy season in Japan. 答2: 日本の梅雨ですから。 A2: Because it’s rainy season in Japan.
Looking at the English translations, we see that the subtle difference is the use of the word “it’s” at the start of the answer. In English, when you’re asked to state a reason in response to question, it’s acceptable to answer with “it’s because” or just “because”. The only difference is that when you just use “because” you are technically omitting the situation and just stating the reason. The same is true in Japanese. With that in mind, A2 could be rewritten int eh following way:
答2: 日本の梅雨ですから、毎日雨が振っています。 A2: Because it’s rainy season in Japan, it has been raining everyday.
In any case, you are probably OK to use からです (karadesu) or ですから (desukara) when answering a question for which a reason has been asked. Just be aware that that there is a subtle difference between the two. But in situations where you are making a statement of the (situation)。 (explanation) から。form, then the correct one to use is ですから (desukara).
There are other types of sentences in Japanese that ends with から (kara) which are unfinished sentences. You will encounter these often. What is interesting about them is that depending on what the speaker is trying to convey, just ending with から (kara) implies the rest of the unfinished sentence. I have written all about this type of sentence here.