Breakdown of Ich bin stolz auf meinen Erfolg.
sein
to be
ich
I
auf
on
mein
my; (masculine or neuter, nominative)
Questions & Answers about Ich bin stolz auf meinen Erfolg.
Why isn't the adjective stolz inflected to show gender, number or case?
Because when an adjective follows a form of sein (to be) and describes the subject (predicative position), it remains in its base (uninflected) form.
Why is the preposition auf used after stolz? Could I use von or another preposition?
The fixed expression stolz auf translates to "proud of." Other prepositions like von don't collocate here. You must use auf plus the accusative to express the object of pride.
What case does the preposition auf require in this sentence?
With stolz auf, auf always takes the accusative case, so you have auf meinen Erfolg.
Why is the possessive pronoun mein written as meinen here?
Erfolg is a masculine noun (der Erfolg) and since auf governs the accusative, the masculine singular form of mein is meinen.
Could I say "Ich bin stolz in meinem Erfolg" instead?