結果の so と目的の so thatSo for Results, So That for Aims
接続詞 / Conjunctions
so は「だから」で結果を、so that は「〜するために」で目的を表します。見分ける手がかりは後ろの助動詞。so that の節にはたいてい can / could / will / would が入ります。I left early so that I could catch the train.(乗るために)/ I left early, so I caught the train.(だから乗れた)。この項が扱うのは「節で目的を言う形」で、to 不定詞で目的を言う形は「目的の to」の項にあります。
So means and that's the result; so that means in order to. The tell is the modal that follows: a so that clause almost always carries can, could, will, or would. Compare "I left early so that I could catch the train" with "I left early, so I caught the train." One states an aim, the other reports an outcome. This entry covers purpose expressed as a clause; purpose expressed with a to-infinitive has its own entry.
起きたことか、狙ったことか
What Happened, or What You Were Aiming At
結果の so は等位接続詞で、前後の文を対等につなぎます。目的の so that は従属接続詞で、後ろの節を「狙い」として従えます。厄介なのは、会話では so that の that がよく省かれること。I left early so I could catch the train. のように that が消えると、形の上では結果の so と見分けがつきません。そのとき助かるのが can / could の存在です。
Result-so is a coordinating conjunction: it sets two statements side by side. Purpose-so-that is subordinating: it hangs an aim off the main clause. The awkward part is that speech drops the that all the time. Once "I left early so I could catch the train" loses its that, the shape no longer tells you which one you're reading. That's when the modal earns its keep.
助動詞が目印The modal is the tell
I left early so that I could catch theなぜ the なのか【決まった場所・乗り物】the station / the bus のように、話し手と聞き手の生活で「あの一つ」に決まる施設や便を指す。 train.
電車に間に合うように、早く出た。
could があるので目的。間に合ったかどうかは言っていない。Could marks the aim. Whether the train was caught isn't stated.
I left early, so I caught theなぜ the なのか【決まった場所・乗り物】the station / the bus のように、話し手と聞き手の生活で「あの一つ」に決まる施設や便を指す。 train.
早く出た。だから電車に間に合った。
助動詞なしで過去の事実。結果を報告している。No modal, plain past. This reports what actually happened.
Speak up so everyone can hear you.
みんなに聞こえるように、大きな声で。
that が省略された目的の型。can があるので目的と分かる。A purpose clause with that dropped. Can gives it away.
so(結果・等位)
前にコンマを置くのが基本。so の節だけを文の前半へ動かすことはできない(× So we ate at home, the shop was closed.)。前をピリオドで切って So で文を始めるのは、会話でも文章でも普通。Usually takes a comma before it, and its clause can't move to the front (no "So we ate at home, the shop was closed"). Closing the previous sentence and opening a new one with So is perfectly normal, in speech and writing alike.
The shop was closed, so we ate at home.
店が閉まっていた。だから家で食べた。
so that(目的・従属)
コンマは置かない。節ごと文頭に出すこともできる。No comma before it, and the whole clause can front.
So that everyone could join, we moved the meeting online.
全員が参加できるように、会議をオンラインにした。
よくある間違い / Common Mistake
×I left early for catching the train.
電車に間に合うように早く出た。(のつもりで)
○I left early to catch the train.
電車に間に合うように早く出た。
人の行動の目的には for + -ing を使いません。for + -ing は道具や物の用途を言う型です(a knife for cutting bread =パンを切るためのナイフ)。人が何かを狙って行動する場合は to不定詞。狙いの主語が文の主語と違うときだけ so that + 文にします。so that everyone could join のように、参加するのが everyone で文の主語ではない場合です。
For plus -ing doesn't express a person's aim. That pattern states what a thing is used for, as in "a knife for cutting bread." When a person acts with an aim in mind, use a to-infinitive. Switch to so that plus a clause only when the aim belongs to someone other than the sentence's subject, as in "so that everyone could join," where the joining is done by everyone.
in order to ...〜するために目的の硬い言い方。to だけで足りるので、書き言葉で明示したいときに使う。The formal way to state an aim. A plain to does the job, so save this for writing.
so as not to ...〜しないように否定の目的。to不定詞で not を入れる位置がここになる。A negative aim. This is where the not goes in the infinitive pattern.
so ... that ...とても〜なので〜だ程度と結果の型。so の直後は形容詞か副詞。Degree plus consequence. An adjective or adverb sits right after so.
That's why ...だから〜なんだ結果の so を2文に割った形。会話で頻出。Result-so split across two sentences. Very common in speech.
まとめ / Summary
so =結果、so that =目的。So reports a result; so that states an aim.
that が省かれても、can / could があれば目的。Even with that dropped, can or could marks a purpose clause.
人の行動の目的は to不定詞。for + -ing は使わない。A person's aim takes a to-infinitive, never for plus -ing.
so の直後が形容詞なら「とても〜なので」の別の型。An adjective right after so means you're in the degree pattern instead.