〜出す details
write + suddenly start doing
kaki dasu
suddenly start doing (often uncontrolled)
meaning: write all of a sudden
子供が道路に向かって走りだす。
kodomo ga douro ni mukatte hashiri dasu.
The child runs all of a sudden toward the road. neutral
見て見て、赤ちゃんが歩き出したよ！
mite mite, akachan ga arukidashita yo!
Look, look, the baby started walking! casual
- past
- polite
Examples
suddenly start doing — the action bursts into motion, often without the subject's control
子供が道路に向かって走り出した。
kodomo ga douro ni mukatte hashiridashita.
The child ran all of a sudden toward the road. neutral
見て見て、赤ちゃんが歩き出したよ！
mite mite, akachan ga arukidashita yo!
Look, look, the baby started walking! casual
会議中に社長が突然笑い出されましたので、一同驚きました。
kaigichuu ni shachou ga totsuzen waraidasaremashita node, ichidou odorokimashita.
In the middle of the meeting the president suddenly burst out laughing, to everyone's surprise. formal
Formation
{V-masu-stem}だすattaches to ます-stem
Notes
笑い出す all fit; a scheduled, agentive start (授業を始める) stays with
始める, never ×授業を出す.
Related patterns
Similar
始める takes the volitional mood fine (書き始めよう, "let's start writing" — a deliberate plan); 出す almost never does (×書き出そう) because it names an onset nobody decided on, only noticed.
Both mark an onset mid-event, but 出す commits — the action is fully underway and often out of anyone's control (降り出す, it started raining in earnest), while かける stalls right at the threshold and can stop there (言いかけてやめた, "he started to say it and then stopped").