Learn Hardcore German: Der Autor, dessen Roman ich gerade ausleihe, schreibt sehr spannend. - The author whose novel I am borrowing right now writes very thrillingly.

dessen is the genitive relative pronoun referring back to der Autor, indicating possession. It translates roughly as whose in English (“the author whose novel…”).

Why is dessen in the genitive case, and not in the nominative or accusative?

Because you are expressing a relationship of ownership (the novel of the author). In German, possession is shown by the genitive, so you need a genitive relative pronoun here.

Could you use deren instead of dessen?

No. deren is the genitive relative pronoun for feminine or plural antecedents. Since Autor is masculine, you must use dessen.

What noun does dessen refer to?

It refers directly to der Autor (masculine singular) from the main clause. So the full meaning is “the author whose novel...”.

Why is the finite verb ausleihe at the very end of the relative clause?

Because German subordinate clauses (including relative clauses) follow verb-final word order. Here, dessen Roman ich gerade ausleihe places ausleihe at the end.

Why are commas used around the phrase dessen Roman ich gerade ausleihe?

In German, every subordinate clause—including relative clauses—must be separated from the main clause by commas.

What does ausleihen mean, and how is it different from leihen?

ausleihen means “to borrow” something from someone else.
leihen can mean “to lend” or “to borrow” depending on context, so ausleihen makes it clear you are borrowing.

What is the role of gerade in ich gerade ausleihe?

gerade is an adverb meaning “right now” or “currently.” It sits before the verb in the mid-field and indicates the action is happening at this moment.

Why is schreibt in the present tense, and what exactly does sehr spannend describe?

schreibt is present because it describes either a habitual action (the author writes in a thrilling style) or a general characteristic.
sehr intensifies the adjective spannend, so sehr spannend means “very exciting” or “highly suspenseful.”