I oftentimes got confused about my girlfriends usage of wenn and als, so I think it makes sense to write some short article to explain the difference between wenn and als.

Wenn is used for present events and the future while als is used for the past. Wenn is also used in the past, for repeated events. When using wenn in the past Germans add some other words to it to so you should avoid using only wenn, while talking about the past.

When learning German you will get told the above mentioned rule, but you will not get thought that Germans, except for in books, almost never use pureply wenn, when describing events of the past.

Since this can lead to a lot of misunderstandings I want to shortly summarize when you have to use wenn and als.

The Past Is Not The Past

Wenn

There is a difference between past events that happened only once, and past events that happened repeatedly.

The German grammar books usually tell you that with these repeated events, you will have to use wenn. This is correct, except for the fact that we never use wenn alone, when we talk about the past.

It will confuse Germans a lot when you use wenn this way. Instead of using the word alone, we add some complementary words to it, to make sure everyone understands what we are talking about.

You can imagine this as saying, whenever or every time.

Let’s look at some examples.

When I was sitting in the garden, the sun was always shining.
Wenn ich im Garten saß, schien immer die Sonne.

The above mentioned sentence is grammatically correct, but it might confuse Germans. Usually Germans would phrase this in another way:

Immer wenn ich im Garten saß, schien die Sonne.
Whenever I was sitting in the garden, the sun was shining.

Or:

Jedes Mal, wenn ich im Garten saß, schien die Sonne.
Every time I sat in the garden, the sun was shining

These sentences that use the past and only the word wenn, are usually only mentioned in books.

When reading, my brain thinks about the language differently because it is standard German, so I kind of pay attention to things like this.

When talking however, I do not pay attention to this and I do not expect to encounter phrases like this, so I will get confused if someone uses them.

There are also other words that you can add to wenn, when you use it in the past, such as manchmal (= sometimes) and “hin und wieder” (= from time to time).

When I was walking with my dog, the sun was sometimes shining.
Manchmal, wenn ich mit meinem Hund spatzieren ging, schien die Sonne.

When I ran, my foot was hurting from time to time.
Hin und wieder, wenn ich rannte, hat mein Fuß wehgetan.

If you are unsure whether to use wenn or als, just ask yourself if you could substitute when, in the English sentence, by whenever. If you can, you should probably use immer wenn.

When I met my uncle I was confused (you met him for the first time so you cannot use whenever)
Als ich meinen Onkel getroffen habe, war ich verwirrt.

If you want to make sure that you talk understandable German, then try to avoid using wenn alone.

Als

We use als, when we talk about an event in the past that happened only once. However, some Germans like to ignore this and always use als. (You will probably not notice the difference since they will add immer, manchmal, and jedes Mal to it)

If you are unsure try to substitute “when” in the English sentence by “that time”.

Some examples:

When I was swimming for the first time, I was scared.
Als ich das erste Mal geschwommen bin, war ich ängstlich.

When I wrote my mathematics exam, I was very nervous.
Als ich meine Mathematikprüfung geschrieben habe, war ich sehr nervös.

The Present And The Future

In the present, wenn gets used as a conditional statement. So oftentimes when you use wenn in the present, you will be able to substitute it by “if”.

I will visit you when I am ready.
Ich komme dich besuchen, wenn ich fertig bin.

When I have enough money, I will by the car.
Wenn ich genug Geld habe, kaufe ich das Auto

Germans will only use the word wenn in the present, and you cannot use als here. So everytime you talk about the present, you can simply use wenn.

This is also true for the future:

I will cook, when I return home.
Ich werde kochen, wenn ich heim komme.

I will celebrate, when I have the time.
Ich werde feiern, wenn ich Zeit habe.

Questions

In questions, you would also use “when”, to ask for a specific time. In German we use a completely different question word here, so do not get confused by this.

When asking a question, such as: “When will you cook?”, you will have to use the German question word wann. You can easily spot these situations by trying to substitute “when” by “at what time”, or “at which time”.

When will you pick up the kids?
Wann wirst du die Kinder abholen?

When do you return in the evening?
Wann kommst du heute abend heim?

Conclusion

The right usage of wenn and als depends heavily on the time and the situation you are talking about. Even though it might still seem a little bit confusing, you will quickly be able to differentiate between the two words.

When you are unsure of which word you should use, just try substituting “when” in the English phrase with these other words I showed you.

If you do this, you will not have any trouble deciding which word to use and after some time you will intuitively use the right word. All it takes is practice.