ならSi (es cierto que), Si se trata de

なら follows a phrase or noun to express a condition, as in 田中さんが行かないなら、私も行かない (If Tanaka isn’t going, I won’t go either). The なら of それなら is the same particle, but the phrase それなら is used sentence-initially to refer back to something previously mentioned, as in 行かないの？それなら私も行かない (You’re not going? In that case, I won’t go either).

ば and なら are both conditional forms, but with slightly different nuances. ば focuses on the condition itself, 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.'). In contrast, なら has the nuance that the speaker has some reason to believe the condition is likely, e.g. 田中さんが来てくれるなら 'if Tanaka comes (as I expect he might)'.

なら and ばあいは (often in kanji as 場合は) both correspond to 'if', but with different nuances. なら expresses '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'. In contrast, ばあいは means 'in the event that (A)', presenting a possible situation without assumption, e.g. 来る場合は 'in the event that (they) come'.

なら and もし are both used in conditional expressions but have different roles. なら follows phrases to mean 'If it's the case that (A)', often implying the speaker believes it will happen. もし is used at the start of sentences or phrases to emphasize that a hypothetical statement follows, and is often paired with conditionals like なら, ば, or たら, e.g. もし雨なら行かない ('If it rains, I won't go.').

なら is a conditional that follows phrases to mean 'if it's the case that (A)', often implying the condition is likely or assumed. もしも adds emphasis to the hypothetical nature of a situation and is placed at the beginning, e.g. もしも雨なら 'if it were to rain'. It can also appear with でも, e.g. もしも雨でも 'even if it rains' (implying 'I'll still go', etc.).

Both と and なら are conditional expressions, but differ in nuance. と is used for habitual or automatic results, e.g. 春になると花が咲く ('When it becomes spring, flowers bloom.'). なら is used for one-time or assumed situations and implies the speaker believes the condition is likely, e.g. 雨なら出かけない ('If it's going to rain, I won't go out.').

Both としたら・とすれば・とすると and なら express 'if,' but with different nuance. としたら (and its variants) emphasize a strongly hypothetical condition, like the English 'if we suppose that (A)'. In contrast, なら can imply that the speaker believes the condition likely to happen, e.g. 'if it's true that (A)', or 'if it's the case that (A)'.

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.').

こそ and なら can look similar after a noun, e.g. 彼こそできる vs. 彼ならできる, but differ in nuance. こそ is emphatic, suggesting that something someone is 'the one', e.g. 彼こそできる ('He's exactly the one who can do it.'). なら implies a conditional focus, e.g. 彼ならできる ('If it's him we're talking about, he can do it.'), without the nuance of excluding other possibilities that こそ can have.