Breakdown of Ich kenne den Herrn.
ich
I
kennen
to know (somebody/something)
der
who, which, that (relative pronoun; die, das)
der Herr
the gentleman / Mr.
Questions & Answers about Ich kenne den Herrn.
Why does the word for gentleman have an -n at the end (Herrn)?
This is because of N-declension. Some masculine nouns, like Herr (gentleman), add an -n or -en to the end in every case except the nominative (the subject). Since the gentleman is the direct object receiving the action here, we use the accusative case, so Herr becomes Herrn.
Why is the article den instead of der?
The verb kennen (to know) takes a direct object, which must be in the accusative case. For masculine nouns, the definite article changes from the nominative der to the accusative den.
Could I use weiß instead of kenne here?
No, because German has two different verbs for knowing. You use kennen when you are familiar with a person, place, or thing (like knowing a gentleman). You use wissen (which weiß comes from) for knowing facts or information.
Is Herrn also the plural form for gentlemen?
Not quite! The plural of Herr is actually Herren (with an e). So 'I know the gentlemen' would be Ich kenne die Herren. The singular accusative form we see in this sentence just adds an -n to make den Herrn.