たらWhen, From when, Just when, If

たら and と are both conditional forms, but they differ in nuance and usage. たら expresses both 'if' and 'when', and can describe hypotheticals or one-time events, such as 雨が降ったら行きません ('If it rains, I won't go.'). と is used for regular or expected outcomes, as in 春になると桜が咲く ('When spring comes, the cherry blossoms bloom.').

もし and たら are often used together to form conditional ('if') sentences. もし typically comes at the start of a sentence to emphasize the hypothetical nature of what follows, while たら gives the verb its conditional form. For example, もし宝くじが当たったら車を買おうと思います means 'If I win the lottery, I think I'll buy a car.'.

Both あとで and たら can show that one action follows another, but their usage and nuance differ. あとで simply shows sequence, like 'after doing (A)'. たら adds a conditional nuance and can mean 'when' (temporal) or 'if' (hypothetical). Because of this, they are rarely interchangeable.

ば and たら are both conditional forms, but with different nuances. ば emphasizes the condition itself, often with an 'if and only if' feel, e.g. 田中さんが来てくれれば何とかなる ('If Tanaka comes, it'll work out.'). たら sets up an hypothetical condition, which can be followed by a result, comment, or request, e.g. 田中さんが来てくれたら教えてね ('If/when Tanaka comes, let me know.').

Both 上で and たら can describe sequences or conditions, but with different nuance. 上で implies that one action is a prerequisite for another, such as 社長と相談した上で決めましょう ('Let's decide after discussing it with the president.'). たら is more general and covers a wider range of temporal and conditional uses, as in 晴れたら散歩に行こう ('If it's sunny, let's go for a walk.').

なら and たら are both conditional expressions but differ in nuance and usage. なら means 'if it's the case that (A)', often implying the speaker believes it will happen, e.g. 来るなら 'if it's the case that (they) come'. たら covers the ideas of both 'if' and 'when', expressing both hypothetical conditions or guaranteed events, e.g. 駅に着いたら電話してください ('Call me when/if you arrive at the station.').

それなら expresses a response to a condition, as in それなら行きません (In that case, I won’t go). The conditional たら form can also mark conditions at the end of verbs, adjectives, or nouns. それだったら can convey a similar meaning to それなら, but with a slight nuance: それなら assumes the condition will or has happened, while それだったら tends to be more hypothetical.3

たら expresses a condition or hypothetical, and when combined with どう, forms a casual suggestion. For example, 散歩に行ったらどう？ means 'How about going for a walk?'. Similar to the English phrase 'Why don't you (A)?' or 'How about (A)?', it isis common in informal conversation.

てから and たら both convey a sequence of events, but their nuances differ. てから simply indicates that one event follows another. In contrast, たら is similar to the English 'when' or 'if' and suggests that the second event is a result of the first. たら can be used in both hypothetical situations ('if A, then B') and past events ('When I did A, B happened').