In short

These are the last two of Japan’s four conditionals. 〜ば is the logical one - change the final -u of a verb to -eba (書く -> 書けば kakeba) and you get “if X, then Y as a matter of course”: proverbs, formulas, general truths. 〜なら is the discourse one - it picks up something the other person just said or something already in the air, and adds your comment on it (日本へ行くなら、京都がいいですよ). Learn ば’s one restriction on the main clause, and learn that なら reverses the time order of たら, and the four-way system is complete.

The rule

Step 1 - Build ば: the -eba row. Every verb class ends up in -eba; only the route differs.

• Group I (五段) - change the final -u to -eba: 書く kaku -> 書けば kakeba; 話す hanasu -> 話せば hanaseba; 待つ matsu -> 待てば mateba; 買う kau -> 買えば kaeba.
• Group II (一段) - drop る and add れば: 食べる taberu -> 食べれば tabereba; 見る miru -> 見れば mireba.
• Irregulars - する -> すれば sureba; 来る -> 来れば kureba.
• Negatives - every ない-form is an い-adjective, so ない -> なければ: 行かない -> 行かなければ ikanakereba.
• い-adjectives - drop い, add ければ: 高い -> 高ければ takakereba; いい／よい -> よければ yokereba (never ×いければ).
• な-adjectives and nouns - the plain copula だ has no -eba shape; its conditional base is なら, and the ば after it is conventionally dropped, so they take なら(ば): 静か -> 静かなら(ば), 学生 -> 学生なら(ば). (Its formal counterpart である does have one, hence the stiffer 静かであれば, 学生であれば.) The ば is optional and sounds formal, which is exactly why ば and なら are taught together.

Step 2 - What ば means: a logical link, not a schedule. ば says X is the condition under which Y holds. It is the conditional of general rules rather than of particular occasions, so it dominates:

• Proverbs and sayings - ちりも積もれば山となる。 (Chiri mo tsumoreba yama to naru.) Even dust piled up becomes a mountain.
• Instructions and mechanisms - このボタンを押せば、ドアが開きます。 (Kono botan o oseba, doa ga akimasu.) Press it and it opens - always.
• General truths and calculations - 三に四を足せば、七になります。 (San ni yon o taseba, nana ni narimasu.)
• The condition for something to be possible - 時間があれば、できます。 (Jikan ga areba, dekimasu.)

Unlike と (lesson 24), which reports what automatically happens, ば genuinely leaves the condition open: 時間があれば says nothing about whether you have time.

Step 3 - The one restriction on ば, and the two escape hatches. When the ば-clause verb is an action verb with the same subject as the main clause, the main clause may not be a request, command, invitation or statement of your own volition. This is the rule that trips everyone up:

• ×駅に着けば、電話してください。 -> ○ 駅に着いたら、電話してください。
• ×日本へ行けば、写真を撮りたいです。 -> ○ 日本へ行ったら、写真を撮りたいです。

The first escape hatch: the restriction lifts completely when the ば-clause is stative - あります, います, 分かります, a potential form, or any adjective. Those are conditions, not actions, so anything at all may follow:

• ○ 時間があれば、行きます。 (Jikan ga areba, ikimasu.)
• ○ 安ければ、買ってください。 (Yasukereba, katte kudasai.)
• ○ 分からなければ、聞いてください。 (Wakaranakereba, kiite kudasai.)

The second way out is a change of subject: the restriction only bites when both clauses share one, so an action verb is fine as long as someone else performs it - ○ 田中さんが行けば、私も行きます。 (Tanaka-san ga ikeba, watashi mo ikimasu.)

When in doubt with an action verb, use たら. It is never wrong.

Step 4 - The fixed patterns built on ば. These are chunks worth memorising whole.

1. 〜ばよかった - regret about the past, “I should have (done)”. もっと早く出ればよかったです。 (Motto hayaku dereba yokatta desu.) Negative regret takes the negative ば: 言わなければよかったです。 (Iwanakereba yokatta desu.) I shouldn’t have said it.
2. 〜ばいい - “it suffices to”, the normal way to ask for instructions: どうすればいいですか。 (Dō sureba ii desu ka.) What should I do?
3. 〜ばいいのに - a wish about something outside your control, usually with a note of frustration: 雨がやめばいいのに。 (Ame ga yameba ii noni.) I wish the rain would stop.
4. 〜も〜ば、〜も - “both … and …”, listing two properties of one subject: 田中さんはピアノも弾けば、歌も歌います。 (Tanaka-san wa piano mo hikeba, uta mo utaimasu.)
5. 〜ばこそ - “precisely because” - a formal, emphatic fossil. Recognise it; it is drilled at B2 in lesson 61.
6. 〜ば〜ほど - “the more X, the more Y”, as in 練習すればするほど renshū sureba suru hodo. This is the base of the proportion patterns in the next lesson, lesson 52.

Step 5 - Build なら: attach it bare. Noun + なら, な-adjective stem + なら, い-adjective plain + なら, V-plain + なら. There is no だ in front: ×学生だなら -> ○ 学生なら. A の may be inserted for extra explanatory colour (行くのなら, contracted 行くんなら), linking to the んです of lesson 20.

Step 6 - What なら does: it responds. なら takes something already introduced into the conversation - by your partner, or by the situation - and hangs your comment on it. It is the only conditional with this discourse job.

• Picking up what was just said. A: 日本へ行きます。B: 日本へ行くなら、京都がいいですよ。 (Nihon e iku nara, Kyōto ga ii desu yo.) B is not supposing anything; A said it.
• The topic-conditional, “as for X / if it’s X you mean”. ビールなら、冷蔵庫にあります。 (Bīru nara, reizōko ni arimasu.) Someone asked about beer; this is the answer about beer specifically. Compare 田中さんなら、もう帰りましたよ - “Tanaka? He’s already gone home.”

Because なら needs that prior mention, it cannot open a conversation out of nowhere, and it is the wrong choice for a natural event nobody raised: ×雨が降るなら、中止です -> ○ 雨が降ったら、中止です.

Step 7 - The time reversal: なら vs たら. This is the highest-value contrast in the lesson. With たら the main clause always happens after the subordinate one. なら fixes no order at all, which is why the main clause so often lands before the なら-clause event - it is advice about a plan not yet carried out.

• 日本へ行くなら、円を用意したほうがいいですよ。 - get the yen before you go.
• 日本へ行ったら、着物を買います。 - buy the kimono after arriving.

Same two events, opposite order, decided entirely by なら vs たら.

Forms & patterns

Making the ば-form.

What stands in front of なら - nothing extra, and never だ.

Choosing among the four conditionals.

Examples

Common mistakes

• 日本へ行けば、写真をたくさん撮りたいです。 (Nihon e ikeba, shashin o takusan toritai desu.) -> 日本へ行ったら、写真をたくさん撮りたいです。 (Nihon e ittara, shashin o takusan toritai desu.) - the ば-clause is an action verb with the same subject, so a statement of volition is blocked. Switch to たら.
• 学生だなら、割引があります。 (Gakusei da nara, waribiki ga arimasu.) -> 学生なら、割引があります。 (Gakusei nara, waribiki ga arimasu.) - なら attaches straight to the bare noun; the copula だ is dropped.
• 安いければ、買います。 (Yasuikereba, kaimasu.) -> 安ければ、買います。 (Yasukereba, kaimasu.) - an い-adjective drops its い before ければ. The same goes for いい -> よければ, never ×いければ.
• 食べば分かります。 (Tabeba wakarimasu.) -> 食べれば分かります。 (Tabereba wakarimasu.) - Group II verbs drop る and take れば; only Group I verbs shorten to -eba.
• 日本へ行ったら、ガイドブックを買ったほうがいいですよ。 (Nihon e ittara, gaidobukku o katta hō ga ii desu yo.) -> 日本へ行くなら、ガイドブックを買ったほうがいいですよ。 (Nihon e iku nara, gaidobukku o katta hō ga ii desu yo.) - advice about preparing before the trip needs なら; たら would put the shopping after you land.

Tips

• One sentence holds the whole ば restriction: 時間があれば行きます is fine, but 駅に着けば電話してください is not. State in front - anything may follow. Action in front - only a statement may follow.
• なら answers, たら narrates. If you could preface your Japanese with “if you say so” or “in that case”, you want なら. If you are describing your own future timeline, you want たら. This is why なら so often carries よ at the end: it is a comment offered to someone else.
• Beware English “if”. English uses one word for all four; Japanese chooses by main-clause type, generality and time order, not by the English. Working backwards from “if” is the single biggest source of conditional errors at B1.
• ば has a second life outside conditionals. You already meet its negative in 〜なければならない (“must”, lesson 35) and its casual contraction 〜なきゃ, and you will meet 〜ば〜ほど in the very next lesson. Drilling the ば-form pays off far beyond this page.