〜たら for the perfect aspect / completed actions / resultative state

Question

This is something I've noticed for a while but I want to be sure of it. I just encountered the sentence “準備したらおいで。” in context I'm fairly sure this means “Come when you're ready.” and I've encountered it many times. “準備する” however does not mean “to be ready” but “to get ready”, “to be ready” would be “準備している” or “準備ができている” if I not be mistaken.　Thus, I would expect “準備してたらおいで” instead. After all, the character is beckoned to come when being ready, not when getting ready.

I've seen this multiple times “気づいたら” is of course a fixed idiom which I found counter intuitive from when I first saw it, I had expected “気づいていたら” for that meaning, the same with “帰ったら” clearly meaning “when I get home”. Again, I would have expected “帰っていたら”. Indeed “〜ていたら” does not seem to occur at all much and I don't think I've ever seen it.

So does “〜ていたら” simply not occur at all, and as such is the usage one would expect it to have assumed by “〜たら” with the difference being contextual? Can “帰ったら” also mean “when I go home” opposed to always “when I get home” with the difference being from context or does it always mean “when I get home”? and is this simply how “〜たら” works?

Answer 1

As a native Japanese speaker, I use たら without thinking how it works, but たら has multiple roles. According to the link, when たら is followed by a clause showing intent, invitation, request, etc., it usually refers to the time when the said action is complete. For example, 食べたら教えて means "Tell me when you finished eating". You must not use the teiru-form in basic cases. 準備する is a verb that means "to prepare". I think it's a plain action verb like 走る and 食べる. That's why you have to say 準備したらおいで in basic cases.

However, since たら has many roles, we say 準備してたら or 準備できてたら in certain situations. Note that, just as 走っている or 食べている, 準備して(い)る can mean either "is preparing" (progressive) or "has prepared = is ready" (perfective), depending on the context.

• 準備してたらおいで。
  = 準備できてたらおいで。
  If you're (already) ready (now), come (but if you're not ready yet, don't come).
• 旅行の準備してたら古いアルバムを見つけた。
  I was preparing for a trip and found an old album.
• もっと準備してたら成功しただろう。
  If I had been better prepared, I would have succeeded.

Answer 2

We should distinguish たら as a substitute for a simple conditional form ending with 〜ば from the “proper” たら which is not interchangeable with it. (I say “simple” because the 〜ば form is the most straightforward conditional with its focus on whether a certain condition is true or not.)

When the main clause is in non-past tense talking about what someone will or would do under a certain condition, the proper たら is used with a verb that is viewed as an instantaneous action or change. Imagine a point on an imaginary timeline marking the beginning of the condition under which the event of the main clause will or would happen, not a line segment corresponding to the period during which that condition is true. たら specifically puts focus on that one point and that’s the main difference from the 〜ば form. So it has to be 準備（を）したら or 準備（が）できたら. “Upon doing …” might convey this imagery better to English speakers than “if” or “when”.

Another usage of the proper たら is to talk about a discovery or realization someone made upon doing something. The main clause is always in past tense in this usage. The requirement for spontaneity gets relaxed and たら can be used with a 〜ている form, or the verb いる for that matter, as long as it refers to a volitional act. A 〜ている form is understood as an ongoing action at the end of which the event of the main clause happened. The focus of the sentence is placed on that point (i.e. the time of the discovery or realization).

プレゼンの準備をしていたら夜になっていた。

Now, if you see たら used with a 〜ている form in other cases, you can safely assume it is interchangeable with a simple conditional form. 準備（を）して（い）たら is understood as meaning the same as 準備（を）して（い）れば. It simply means if said condition is true. How this 〜ている form is understood is up to the context as is the case with the 〜ば form. The person may be in the middle of some preparation or they may have completed it and are ready now. And that person may be different from the person you are inviting to come.

This usage of たら sounds colloquial and you probably should avoid it in formal writing. Some dialects tend to use this たら more liberally than standard Japanese, which is based on a dialect spoken in or around Tokyo.