Japanese has four conditional forms and they are not interchangeable. This is the most common N4 grammar gap, and it is more approachable than its reputation suggests.
If you learn one, learn たら. It covers the widest range of situations and is rarely wrong.
たら - the general-purpose one
Built from the た-form: 食べた → 食べたら.
Used for: a specific future condition, a hypothetical, or “when” something happens.
- 雨が ふったら、行きません。- If it rains, I will not go.
- 日本に 行ったら、電話します。- When I get to Japan, I will call.
- お金が あったら、買います。- If I had money, I would buy it.
It accepts requests, invitations and intentions in the second half, which the others do not all do. That is why it is the safe default.
と - automatic consequences
Dictionary form + と. Used when A always produces B - natural laws, machines, directions.
- ボタンを 押すと、ドアが 開きます。- If you press the button, the door opens.
- まっすぐ 行くと、駅が あります。- If you go straight, there is the station.
Restriction: you cannot follow と with a request, an invitation or an intention. 押すと、開けてください is wrong.
Because of the machine-and-directions use, と appears frequently in workplace instructions: transport Japanese.
ば - conditions and general truths
Formed by changing the final う-row sound to え-row plus ば: 行く → 行けば, 食べる → 食べれば.
- 安ければ、買います。- If it is cheap, I will buy it.
- 時間が あれば、手伝います。- If I have time, I will help.
Often interchangeable with たら for hypotheticals. It is also the base of ～なければなりません (must), which you already use: the nai-form.
なら - responding to what was just said
Attaches to a noun or plain form, and takes up a topic someone else introduced.
- A: 日本に 行きます。B: 日本に 行くなら、JRパスを 買ったほうが いいですよ。
The distinguishing feature: なら responds. If nobody has raised the topic, なら is usually the wrong choice.
How to sort them quickly
| Situation | Use |
|---|---|
| A always causes B | と |
| A specific future condition | たら |
| A hypothetical or general condition | ば or たら |
| Responding to what someone said | なら |
| The second half is a request | たら (not と) |
How to practise
Write six sentences about your own routine using たら, then rewrite the ones that are automatic consequences with と. That contrast - chosen rather than memorised - is what fixes the distinction.
Then check the forms are secure: they build on the ta-form and the plain form, and they appear on the N4 grammar checklist.