～ては～てはRepeated alternating actions
This pattern presents two or more steps as a cycle that happens again and again. It is especially useful for describing back-and-forth movement or a longer process in which one repeated step leads to another.
How the cycle works
The important idea is recurrence, not simply order. The listener should be able to picture the steps repeating over a period of time, often with the same two stages returning in turn. In a reversible cycle, the order can be shown in both directions.
A back-and-forth cycle
猫は三十分ほど、部屋に入っては出て、出ては入っていた。
For about thirty minutes, the cat kept going into the room and coming out, then going out and coming back in.
AnalyzeThe two directions are reversed in the second half, making the repeated back-and-forth movement explicit.
A longer recurring process
The steps do not have to be exact opposites. They can be stages in a recurring workflow, provided the context makes it clear that the sequence happened repeatedly rather than only once.
締め切り前の三日間は、資料を読んではメモを取り、メモを見ては文章を書き直す毎日だった。
For the three days before the deadline, every day was a cycle of reading the materials and taking notes, then consulting the notes and rewriting the text.
AnalyzeThe three-day period and the reference to each day establish that the workflow was repeated.
In casual conversation
昨日のレポート、なかなか終わらなかったの？
Did yesterday's report take you a long time to finish?
Analyzeうん。二時間も、書いちゃ消し、消しちゃ書いてた。
Yeah. For two whole hours, I kept writing things, deleting them, and writing them again.
Analyze書いちゃ and 消しちゃ are casual contractions of the full forms with the repeated-step marker.
Cycle or representative list?
～ては～ては says that the steps repeatedly follow one another. By contrast, たり～たり gives representative examples of activities and does not by itself claim that they alternate as a cycle.
休みの日は、本を読んだり、散歩したりする。
On my days off, I do things like read books and take walks.
AnalyzeThese are examples of activities; the sentence does not say that reading and walking repeatedly alternate.
More examples
振り子は十分以上、右に揺れては左に戻り、左に揺れては右に戻っていた。
For more than ten minutes, the pendulum kept swinging right and returning left, then swinging left and returning right.
Analyze朝から夕方まで、原稿を印刷しては誤字を見つけ、修正してはまた印刷する作業が続いた。
From morning until evening, the work continued in a cycle of printing the draft, finding typos, making corrections, and printing it again.
Analyze天気は朝から、晴れては曇り、曇っては晴れるのを繰り返している。
Since morning, the weather has repeatedly shifted from sunny to cloudy and back to sunny.
Analyze子どもたちは三十分も、積み木を積んでは崩し、崩してはまた積んで遊んでいた。
For a whole thirty minutes, the children played by stacking the blocks, knocking them down, and stacking them again.
Analyze研究チームは数か月にわたり、仮説を立てては実験し、結果を分析しては仮説を修正した。
Over several months, the research team repeatedly formed hypotheses, ran experiments, analyzed the results, and revised the hypotheses.
Analyze彼女は一週間、店へ通っては値段を確かめ、家に戻っては予算を計算していた。
For a week, she kept going to the store to check the price, then returning home to work out her budget.
Analyze