wenn vs ob (if/whether)

English uses one little word, if, for two completely different jobs, and German splits that job between two words: wenn and ob. Getting this right is one of the highest-payoff fixes at B1, because the error is so frequent and so audible — Ich weiß nicht, wenn er kommt is one of the most common mistakes English speakers make in German, and it sounds distinctly wrong to a native ear.

The good news: there is a clean, mechanical test that almost never fails. Read on, and you will be able to choose correctly even in sentences you have never seen.

The core distinction in one sentence

Use ob when "if" means whether (it introduces an indirect yes-or-no question); use wenn when "if" sets up a condition, or when it means when(ever) in time.

ob = whether (indirect yes/no questions)

ob introduces an embedded question whose answer is yes or no. The main clause typically expresses not-knowing, asking, wondering, doubting, or checking: I don't know..., I'm wondering..., She asked..., It depends on.... Behind every ob-clause there is a hidden direct question: "Is he coming?" → Kommt er? That buried yes/no question is the signature of ob.

Notice that in every one of these, you could swap English "if" for "whether" and the sentence still makes sense. That is the test, and we'll formalize it below.

wenn = condition (real "if") and time ("when/whenever")

wenn has two senses, and crucially neither can be replaced by "whether."

1. Conditional wenn — "if X (is true / happens), then Y." This is the if of cause-and-effect and hypotheticals.

2. Temporal wenn — "when" or "whenever," for present/future events or repeated past events.

The whether-test (your one reliable rule)

Before you write "if" in German, ask one question:

Can I replace "if" with "whether" and keep the meaning?

• Yes → ob. ("I don't know whether he's coming." ✓ → ob)
• No → wenn. ("Whether it rains, I'll stay home." ✗ — meaningless → wenn)

This works because English "whether" only ever marks a yes/no alternative — exactly the job German assigns to ob. Conditional and temporal "if" reject "whether" outright, so they fall to wenn by elimination.

Both are subordinating: verb goes to the end

wenn and ob are both subordinating conjunctions, so the conjugated verb moves to the end of the clause, and a comma separates the clause from the main clause.

When the wenn-clause comes first, the main clause begins with its verb (verb-second rule counting the whole subordinate clause as position one) — often joined by dann or so:

Why English speakers go wrong here

English collapses two logically distinct ideas into one word. Compare:

• Whether-if answers a yes/no question: I asked if [yes or no?] she was home.
• Conditional if states a precondition: If [precondition holds] she'll come.

Because both surface as "if," English speakers don't feel the difference, so they reach for the conditional word wenn for both — producing the classic error Ich weiß nicht, wenn er kommt ("I don't know if/when he comes"), which a German hears as either "I don't know when he comes" or simply as broken. German never lets these two meanings share a word, which is exactly why the whether-test is so powerful: it forces the hidden distinction back into the open.

Edge cases worth knowing

1. "if ... or not" is always a yes/no alternative → ob, often with ob ... oder nicht.

2. "as if" = als ob (or als wenn / als + subjunctive). The fixed phrase als ob keeps its ob.

3. "even if" = (sogar) wenn / selbst wenn / auch wenn — still conditional, so wenn.

4. Indirect wh-questions (who/what/where/when) do not use ob — they keep their question word (wer, was, wo, wann). ob is only for the yes/no kind.

That last example is the trap that mirrors the classic error: wann (when), not wenn, and not ob. "When he's coming" is a wh-question, not a yes/no question, so neither ob nor wenn fits.

Common Mistakes

Key Takeaways

• ob = "whether" — an indirect yes/no question after not know, ask, wonder, doubt, depend on.
• wenn = conditional "if" (if it rains) and temporal "when/whenever" (when I get home).
• The whether-test decides every case: if "whether" fits the English, use ob; otherwise use wenn.
• Both send the verb to the end and take a comma.
• Don't confuse wenn ("if/when") with wann ("when?" — for asking and for indirect when-questions).