Breakdown of Haben Sie den Präsidenten gesehen?
Sie
you (formal)
haben
to have
sehen
to see
der
who, which, that (relative pronoun; die, das)
Questions & Answers about Haben Sie den Präsidenten gesehen?
Why is there an "-en" at the end of Präsidenten if it's only one president?
Der Präsident belongs to a special group of masculine words called "weak nouns" (this is the N-Declension rule you are currently learning). These nouns add an -n or -en ending in every case except when they are the subject (Nominative). Because the president is the direct object being seen here (Accusative case), Präsident becomes Präsidenten. Many masculine nouns ending in -ent, like der Student or der Patient, follow this exact same rule.
Since the weak noun ending is -en, how do I know this isn't plural?
You have to look at the article! The word den is the masculine singular article for the Accusative case, so we know there is only one president. If the sentence were about multiple presidents, the plural Accusative article die would be used instead: Haben Sie die Präsidenten gesehen?
Why is Sie capitalized in the middle of the sentence?
A capitalized Sie is the formal "you", used when speaking politely to strangers, older people, or authority figures. If it were a lowercase sie, the sentence would mean "Have they seen the president?" (If you wanted to say "Has she seen the president?", the verb would also have to change to Hat sie...).
Why are the verbs Haben and gesehen separated?