Tara Conditional (~tara)

~たら is formed by adding ら to the past tense (ta-form) of a verb, adjective, or noun + だった. It is the most commonly used and versatile conditional in Japanese, suitable for most 'if/when' situations.

~たら can express hypothetical conditions (もし雨が降ったら — if it rains), temporal sequences (家に帰ったら — when I get home), and discovered situations (窓を開けたら猫がいた — when I opened the window, there was a cat). This last usage — discovering something unexpected — is unique to ~たら among the conditionals.

Compared to other conditionals: ~たら is the safest and most flexible choice. It works with volitional actions in the result clause, past events, requests, and suggestions. When in doubt about which conditional to use, ~たら is usually acceptable.