I'm so confused, which is the correct sentence (I will become a doctor):
- Ich werde ein Arzt
- Ich werde ein Arzt sein
as the comments on the OP already stated: they are both correct
.... but they also have slight differences in meaning/tempus
ich werde ein Arzt
literal translation: i'm becoming a doctor, ie. he/she is still studying it.
note: more often than not the article ein would be dropped here
on the other hand: this can also be used as a shortened version of the the 2nd sentence, but then it's not quite correct
Ich werde ein Arzt sein
literal translation: i will be a doctor.
again, ein may be dropped here, but in this case it is common to have it. Having it emphasizes somewhat that he will be a doctor of some sort without naming it. Dropping it generalizes that and puts emphasis on the title.
Most common would be: "Ich werde Arzt."
Later you will say, "Ich bin Arzt."
No article. It's as if professions are a kind of quality.
"Ich bin ein Arzt" might mean something like "I am one of the people who are doctors and hence must be expected to do what they do", and not so much "I have acquired the skills and qualifications that make one a doctor".
This is Präsens (similar to English present tense). You are describing a transformation that is happening right now (not in the future). You can translate it as:
I'm becoming a doctor.
I turn into a doctor.
I transform into a doctor.
The word werde (a form of werden) is used as full verb here. It has a semantic meaning, and this meaning is to become (something), to turn (into something), to transform (into something). In this sentence there is no auxiliary verb.
To point out that this sentence is present tense, you could add a temporal adverb:
Ich werde jetzt ein Arzt.
I'm becoming a doctor now.
This can be confusing:
In German the grammatical tense Präsens also can be used to describe things that happen in the future:
Ich kaufe morgen Milch. (same meaning as "Ich werde morgen Milch kaufen.")
I'm buying milk tomorrow. = I will buy milk tomorrow.
So you also can say in German:
Ich werde in fünf Jahren Arzt.
I'm becoming a doctor in five years. = I will become a doctor in five years.
This still is grammatically Präsens, but semantic we are talking about a transformation that will happen in the future.
This is Futur I (future tense). You are talking about a state that will exist in the future. This state isn't the case now. You can translate it as:
I will be a doctor.
There are two verbs in this sentence. The full verb is sein (to be) And since there are other verbs in the predicate, then the full verb is not allowed to occupy position 2. It has to stand at the very end of the sentence.
The other verb is werde (a form of werden). Here it is used as an auxiliary word without any semantic meaning. It is here only for syntactical/grammatical reasons: It indicates future tense. And it's the verb that has to occupy position 2.
There are at least three possible reasons for the confusion:
Let's consider them one at a time:
I will become a doctor
literally translates to
Ich werde Arzt werden (without
In the first occurence of werden (werde), it serves as auxiliary verb of the future tense. In the second occurence, it is a full verb, meaning to become.
Regardless of the literal translation, the English expression I will become conveys in fact a meaning like ich werde sein (future of German to be). In German, however, you would express the same thing with ich werde (Präsens of German to become). To better understand how werden is used, you could think of becoming as an process that starts in the moment you make the decision. Thus, in German you talk about it like it's already happening.
However, in German, the tenses aren't strictly used chronologically anyways. So even if you would start the whole process of becoming a doctor only in the (near or at least foreseeable) future, you would simply say Ich werde Arzt instead of Ich werde Arzt werden due to tense usage.