[化学論文のための英語講座] 第85回：「Because」と「Since」と「As」 Because, Since, and As
2025年11月25日
(English version is here.)
従属接続詞であるbecause, since, as は「なので」という意味があります。sinceは時間の意味もあり、asは時間と比較の意味もありますが、今回のテーマでは「なので（理由）」の意味で使用しています。because, since, asは同じ意味を表しますが、使い方が少し異なります。この差の根拠は、聞き手が理由を知っているか否かにあります。相手が「知らない」場合はbecause、「知っている」場合はsince, asを使います。論文においては、読み手が知っているか知らないかは自明ではないので、この使い方は報告書や論文よりも、書面による通信や会話においてより重要になるかもしれません。
例文を見てみましょう。
1. Because the enol ether was formed quantitatively, the product could be used in the next reaction without further purification.
和訳：エノールエーテルが定量的に生成されたため、生成物はさらに精製することなく次の反応に使用できた。
ここでは「since」でも「as」でも問題なく使えますが、「because」の方が明確な因果関係を表します。聞き手が背景（原因、理由）を知っているかは、自明ではありません。
2. Since we are working towards related target molecules, perhaps we should collaborate on synthesis of common intermediates.
和訳：我々は関連する標的分子に取り組んでいるので、共通の中間体の合成で協力する必要があるかもしれない。
ここでは「since」が現れるので、聞き手が背景（原因、理由）を知っているかもしれません。代わりに「as」を使うとほぼ同じ意味を伝えられます。
「because」は事実を述べるのに対し、「since」と「as」は提案に近い意味合いがあります。
重要点！！主節と従属節を持つ完全な文章を書くようにしてください。Because, since, as は節をつなげるので、２節以上が必要です。
以下の例文を見てみましょう。
3. Because the α proton is acidic.
和訳：αプロトンは酸性なので・・・
これは不完全な文章です。
4. The enolate forms easily because the α proton is acidic.
または
Because the α proton is acidic, the enolate forms easily.
和訳：αプロトンが酸性であるため、エノラートは容易に形成される。
両方とも正しいです。
感覚的には「because」は「Aの原因や理由はB」、「since」は「AがあってからB」、「as」は「Aと同時に、またはAと同じようにB」だと考えられます。Because, since, asの使い分けは厳密な規則ではなく、傾向です。混ぜて使っても特に目立つことはありません。
次回もどうぞお楽しみに。
The subordinating conjunctions because, since and as mean "as a consequence". Since also has a meaning of time, and as has a meaning of time or comparison, but for this theme we are using them to mean cause. Because, since and as represent the same meaning, but use differs slightly. The basis for this difference is whether the listener knows the reason or not. When the listener does not know, because, and when the listener does know, since or as are often used. In most written compositions, whether the reader knows or not is unclear and hence, this is more important in conversation or written correspondence.
Let us look at a few examples.
1. Because the enol ether was formed quantitatively, the product could be used in the next reaction without further purification.
Since or as would also work here, but because expresses a clearer causal relationship. Whether the reader knows the background (cause, reason) is not obvious.
2. Since we are working towards related target molecules, perhaps we should collaborate on synthesis of common intermediates.
Since appears here and thus, the reader probably knows the background (cause, reason). Alternatively, using as would convey largely the same meaning. Because states a fact, whereas since and as are closer to a suggestion.
Important! Be sure to write complete sentences with a main clause and a subordinate clause. Because, since, and as join clauses and hence, at least two clauses are needed.
Take a look at the following example.
3. Because the α proton is acidic...
This is an incomplete sentence.
4. The enolate forms easily because the α proton is acidic.
or
Because the α proton is acidic, the enolate forms easily.
Both are correct.
Intuitively, because can be thought of to be "the cause or reason for A is B", since to be "after A, B occurs", and as being "B at the same time as A, or in the same way as A". The distinction between because, since, and as is not a strict rule, but a tendency. Mixing them does not particularly stand out.
We look forward to seeing you next time.