〜たら as a completion-focused 'when/if', and a discovery marker
Quick refresher: 〜たら = plain past + ら. 食べた → 食べたら, 行った → 行ったら, さむい → さむかったら, やすみ → やすみ だったら. Today we go past the basics. 〜たら has a feel the other conditionals don't: it's about completion — once X is finished, then Y. That's why it slides easily between 'if' and 'when'. And in the past tense, it does something special: 家 に かえったら、だれ も いません でした。 = 'When I got home, nobody was there.' That's the discovery reading — you do X, and then discover Y. We'll also start lining 〜たら up against 〜ば and 〜なら so the next two lessons land cleanly.
The completion feel
The reason 〜たら translates as both 'if' and 'when' is that it doesn't pick — it just says 'once X is done'. しごと が おわったら、ジム に 行きます。 = 'When work ends, I'll go to the gym.' (planned — 'when'). 雨 が ふったら、行きません。 = 'If it rains, I won't go.' (uncertain — 'if'). Same form, two readings, decided by context. The shared feel: X completes first, then Y. This is why 〜たら is the most common conditional in everyday speech — it doesn't commit to 'if' or 'when', it just sequences.
The discovery reading — past 〜たら + past result
Here's the trick that's new today. When the main clause is in the past, 〜たら stops meaning 'if/when' in the future sense and starts meaning 'when I did X, (it turned out that) Y'. 家 に かえったら、だれ も いません でした。 = 'When I got home, nobody was there.' The speaker came home (X), and upon arriving, discovered nobody was there (Y). まど を あけたら、雨 が ふって いました。 = 'When I opened the window, (I saw) it was raining.' The Y clause is something the speaker noticed / found out as a result of X. Y is not something the speaker caused — it was already true; the X-action just revealed it. English often uses 'when I X, I found that Y' or 'when I X, Y' for this.
Why this isn't 'after'
Past 〜たら ('discovery') and 〜てから ('after, and from then') and 〜た 後 で ('after') all touch sequencing — but they're not interchangeable. 家 に かえった 後 で、ばんごはん を 食べました。 = 'After getting home, I ate dinner.' (You came home, then you did the next thing.) 家 に かえったら、だれ も いません でした。 = 'When I got home, nobody was there.' (You came home, and discovered a state.) Use 〜たら when the second clause is something you noticed or that happened on its own. Use 〜た 後 で / 〜てから when the second clause is your next action.
〜たら vs. the others — a first sketch
All four Japanese conditionals (〜たら, 〜ば, 〜と, 〜なら) overlap, but each has a default feel. 〜たら = 'once X is done, …' — completion-focused; works for both single events and one-shot futures. 〜ば (next lesson) = 'given X, …' — natural / general / hypothetical; great for universal truths and 'if it were the case'. 〜なら (lesson after) = 'if it's the case that X (which we just brought up), …' — picks up a topic from context. 〜と (later) = 'whenever X, Y inevitably' — mechanical / habitual. Today, just remember 〜たら = completion.
Form recap & a pattern check
Verbs: plain past + ら. 行く → 行った → 行ったら. 食べる → 食べた → 食べたら. する → した → したら. 来る → 来た → 来たら. い-adj: さむい → さむかったら. な-adj / nouns: しずか → しずか だったら, やすみ → やすみ だったら. Negatives: 行かない → 行かなかった → 行かなかったら. The whole conditional ride uses one move: build the plain past, then tag ら.
もし — softening the 'if'
もし ('if perhaps') marks the front of an iffy conditional: もし 時間 が あったら、来て ください。 = 'If (perhaps) you have time, please come.' もし is optional — leaving it off doesn't break anything; adding it just signals to the listener 'I'm in hypothetical mode.' Don't use もし with the discovery reading (past + past) — that's a real event, not a hypothesis.
