Maybe. A big doctor not always is great and viceversa.
That in English.
In Spanish big (grande) means tall, great, extraordinary and sometimes, grown up/adult.
I find Arabic similar to Spanish language in several aspects.
Some things in Spanish were inherited from or influenced by the Arabs who dominated the Iberian peninsula for 8 centuries.
So, it would be great (big ) and probably easier to learn, if Duolingo had Arabic in Spanish for Spanish speakers.
Whether big or great, why couldn't it mean "My son, the great doctor..." And please don't say that there's a full stop. As someone said earlier, you don't have punctuation in oral communication. Does that mean that you don't know what it means until they have finished the sentence?
2- Exactly, I was about to write this. When the sentence is literally "my son A great doctor" you should think of a hidden verb (to be) giving the sentence the following equivalent meaning: my son is a doctor. However, When the sentence is literally "my son THE great doctor" this depends on the rest of the sentence if there is a verb you take it, if not you then you should think of a hidden verb (to be)
I cannot say I have understood your point of view totally. but I hope you will find the following useful:
1-In German, the verb comes at the end of the sentence. This means you cannot understand the full meaning until the speaker finishes his sentence. In Arabic, sometimes you cannot understand the full meaning until the speaker finishes his sentence, this is not because the verb is at the end but because verb (to be) might be hidden or unspoken.