出す【だす】

出す after the ます-stem of a verb says the action starts, usually suddenly and without warning: なく泣く becomes なきだす泣き出す, "burst into tears". The compound conjugates like 出す on its own: はしりだした走り出した, はしりださない走り出さない, はしりだして走り出して.

出す or 始める

Both mean "start doing". 出す puts the weight on the moment the action breaks out; はじめる始める simply says it began, and suits a planned or gradual start.

出す reports a start that happens or has happened. It does not go into a request, an invitation or a statement of what you intend to do; 始める does.

• × さあ、食べ出しましょう → さあ、食べ始めましょう
• × ここから書き出してください → ここから書き始めてください
• × 明日から日記を書き出すつもりだ → 明日から日記を書き始めるつもりだ

Usage notes

These go beyond "start suddenly".

"Out"

In some compounds 出す keeps its own meaning, "out": とりだす取り出す is take out, とびだす飛び出す jump out, にげだす逃げ出す run away. These are separate words, and a dictionary lists them.

Coming up with something

かんがえだす考え出す and つくりだす作り出す mean "think up" and "create". 考え出す can also mean "start thinking", and the sentence decides which.