ばif; provided that
ば is for what a result depends on: "if" with the weight on the condition. It is the "if" of advice, of instructions and of どうすればいいですか, "what should I do?"
If you practice every day, you will gradually improve.
If the weather is good, you can see the mountains from the roof.
If you have any questions, please ask at reception.
Verb
行く → 行けば 食べる → 食べれば する → すれば 来る → 来れば
The last kana changes to its え sound, and ば follows: 買う → 買えば, ある → あれば. Godan verbs (う-verbs), ichidan verbs (る-verbs) and the two irregular verbs all do this.
い-adjective
安い → 安ければ いい → よければ
い becomes ければ.
Negative
行かない → 行かなければ 安くない → 安くなければ
ない becomes なければ.
Noun, な-adjective
雨なら 静かなら
No ば form in everyday speech: なら does the job.
What it takes
The result is already in view, and ば names what will bring it about.
What should I do to open this file?
You can open it if you use this app.
If we hurry, we can still make it.
ば or たら?
Often either will do. たら is the more common in conversation.
If it's cheap, I'll buy it.
The same, leaning on the condition: it depends on the price.
A request, an invitation or a plan can follow ば when the first half says how things are: あれば, できれば, なければ, an adjective. After something you do, they take たら.
If you don't understand, please ask.
Not said: 駅に
(Please call when you arrive at the station.)
Arriving is something you do, and after an action ば leads to a result.
Please call when you arrive at the station.
First you arrive, then you call, this once. たら takes the request.
Things people say
よければif you like
Please use this, if you like.
よかったら is its more casual twin.
できればif possible
If possible, please reply by tomorrow.
The four ways to say "if"
Often more than one would fit, but each has its own job. One heater, four sentences, ば first.
You can turn on the heating if you press this button.
たらN4
The everyday "if" and "when": one thing happens, then the other. Of the four, the safe choice when you are not sure.
If it is cold, please turn on the heating.
とN4
For what follows by itself: how machines work, what the seasons bring, habits, directions. Never followed by a request, an invitation or a plan.
When you press this switch, the heating comes on.
ならN4
Takes up what was just said or supposed, and answers it. Nothing has to happen first, so the answer is often advice about what to do beforehand.
If you are going to use the heating, please close the window first.
Close neighbours
なければならないN5
"Must" is this ば: "if I don't, it won't do".
I promised, so I must return the book by tomorrow.
Asking what to do, or how. どうすれば and どうしたら mean the same here.
How should I get from the airport to the hotel?
Check yourself
1Which sentence sounds natural?
Choose an answer to see why.
2"If it rains tomorrow, the game is off."
明日
Choose an answer to see why.
3Which one fits?
バスに
Choose an answer to see why.
More detail
であれば
In notices and formal writing, a noun or a な-adjective takes であれば where everyday speech has なら.
If you are a member, you may use this room.
すりゃ, なけりゃ
In rough, casual speech れば can shrink to りゃ: すれば → すりゃ, なければ → なけりゃ.
What am I supposed to do?
More sentences
If the conditions change, the answer changes too.
If the parts arrive by tomorrow, we can do the repair on schedule.
If the price is low, more people will probably use it.
If you have identification, you can register on the spot.
If you take this medicine, you will soon feel better.