At its core, "zu" is a preposition that typically translates to "to" in English. It’s often used to indicate direction towards a place, person, or goal. For instance, in the sentence "Ich gehe zu meiner Freundin" (I am going to my friend's house), "zu" conveys the direction or destination. This usage of "zu" is straightforward and one of the most common. However, "zu" is also used with verbs to express an infinitive form, similar to the English "to" before a verb. For example, in the sentence "Es ist schwer zu verstehen" (It is difficult to understand), "zu" is placed before "verstehen" to create the infinitive form.
The use of "zu" becomes more complex when it is paired with certain verbs, as not all verbs require "zu" before their infinitive.
One key rule is that "zu" is not used with modal verbs. Modal verbs in German, such as "können" (can), "müssen" (must), and "wollen" (want), do not require "zu" before the infinitive verb they govern. These verbs already imply the infinitive action directly, so the addition of "zu" is unnecessary and incorrect. For example, in the sentence "Ich will Deutsch lernen" (I want to learn German), "lernen" (to learn) follows directly after "will" (want) without the need for "zu." This pattern holds true for all modal verbs, ensuring that "zu" is omitted in such contexts.
Similarly, "zu" is not used after verbs that describe preference or liking, such as "mögen" (to like), "lieben" (to love), or "hassen" (to hate). When these verbs are followed by another verb in the infinitive, "zu" is not included. For example, "Ich mag tanzen" (I like to dance) demonstrates how "tanzen" (to dance) follows directly after "mag" (like), without the inclusion of "zu." This is because the verbs themselves imply the infinitive action, eliminating the need for "zu."
On the other hand, "zu" is required when using certain verbs that govern infinitive clauses, particularly verbs that express attempts, beginnings, or plans. For example, verbs like "versuchen" (to try), "anfangen" (to start), and "vorhaben" (to plan) require "zu" before the infinitive verb. Consider the sentence "Ich versuche, Deutsch zu lernen" (I am trying to learn German). Here, "zu" is necessary before "lernen" (to learn) because the verb "versuchen" (to try) demands it in this context. This rule extends to many other verbs that involve the notion of attempting or planning something, making "zu" an essential element of the construction.
"Zu" also plays a significant role in infinitive constructions with "um zu." The phrase "um zu" is used to express purpose or intention and can be translated as "in order to" in English. For example, the sentence "Ich lerne Deutsch, um nach Deutschland zu ziehen" (I am learning German in order to move to Germany) illustrates this usage. Here, "um" introduces the purpose of the action, while "zu" precedes the infinitive verb "ziehen" (to move).