Wenn, Als, Ob: The 3-Second Trick to Never Mix Them Up Again

"If", "when" and "whether" are three different words in German: wenn, als and ob. English learners mix them up all the time, because English often uses just "when" or "if" for all of them. The good news: you can choose the right one in about three seconds with a simple trick.

The 3-second trick

Ask yourself these three questions in this order:

1. Is it an indirect yes/no question? Then use ob (whether).
2. Did it happen once in the past? Then use als (when).
3. Anything else? Then use wenn (if, whenever, when in the present or future).

Ob: the "whether" word

Use ob when you report a question that can be answered with yes or no. Often there is a phrase before it, like ich weiß nicht (I don't know) or ich frage mich (I wonder).

• Ich weiß nicht, ob er kommt. – I don't know whether he is coming.
• Kannst du prüfen, ob der Laden offen ist? – Can you check if the shop is open?
• Ich frage mich, ob sie Zeit hat. – I wonder whether she has time.

Here English uses "if", which is why learners wrongly say wenn. Test: if you can replace "if" with "whether", it is ob.

Als: one event in the past

Use als for a single event in the past, or for a period of the past that you see as one block.

• Als ich gestern nach Hause kam, war niemand da. – When I came home yesterday, nobody was there.
• Als ich ein Kind war, wohnten wir in Berlin. – When I was a child, we lived in Berlin.
• Als der Film begann, schaltete er sein Handy aus. – When the film started, he switched off his phone.

Wenn: everything else

Wenn covers three situations: conditions ("if"), things in the present or future ("when"), and repeated events in the past ("whenever").

• Wenn es regnet, bleibe ich zu Hause. – If it rains, I stay at home.
• Wenn ich morgen ankomme, rufe ich dich an. – When I arrive tomorrow, I'll call you.
• Immer wenn ich ihn sah, lachte er. – Whenever I saw him, he laughed.

Don't forget wann

The word wann asks about a point in time: Wann kommst du? (When are you coming?) And it stays wann in a reported question about time: Ich weiß nicht, wann er kommt. If you ask "at what time?", use wann.

The verb goes to the end

All three words start a subordinate clause, so a comma comes before them and the conjugated verb jumps to the end of that clause: Ich weiß, dass er kommt follows the same pattern. If you want to refresh how the verb behaves in a normal sentence, read our guide to the verb-second rule.

Common mistakes

• Using wenn for a single past event. Wrong: Wenn ich gestern nach Hause kam, ... Right: Als ich gestern nach Hause kam, ...
• Using wenn for "whether". Wrong: Ich weiß nicht, wenn er kommt. Right: Ich weiß nicht, ob er kommt.
• Using als for a repeated event. Wrong: Als ich ihn sah, lachte er immer. Right: Immer wenn ich ihn sah, lachte er.
• Mixing up als and wie in comparisons. After a comparative, use als: größer als ich (taller than me).

Your turn

Write one sentence for each word: one with ob (something you don't know), one with als (something that happened once last week) and one with wenn (a habit or a plan). Then test yourself with real example sentences and get instant feedback.

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