The Difference between たら・なら・ば

Japanese has a few different ways to say if or when. Sentences that have if in them are called conditional sentences because they tell you something may happen under certain conditions.

行いったら
行くなら
行けば
If (someone) goes

The three examples above all translate to the same thing in English but are not always used in the same situations in Japanese.

～たら

たら is translated as if or when. The reason is that たら shows up in sentences where something is sure to happen and sentences where they are uncertain. Depending on whether we know or not if John is coming the meaning will change.

Also, another important fact about たら is that the conditions need to be met in a sentence with たら before the results of the next sentence can happen. In other words, in the example above John actually needs to come first before I can go out.

～ば

Let’s take another look at the previous sentence but instead replace たら with ば

The sentence means pretty much the same thing.

It is also a requirement that John first comes before I can go anywhere. Here, the difference between たら and ば is that 来れば only means if (John) comes. If we know that John is coming it would be weird to say 来れば. 

Looking into this even further, saying 来くれば instead of 来きたら means that if John does not come then I won’t go.

～なら

Finally, なら is similar to たら and ば but it does not matter if John comes now or later.

なら does not require John to come first before I can go. I may wait for John to come and then leave, or I may decide to leave before he gets here.