You have asked an important question. It presents you with an opportunity to learn the difference between verbs, participles, and infinitives. Neither "fighting" nor "to fight" can act as a verb. Participles and infinitives act as nouns, adjectives, and adverbs. They are flexible and give great descriptive powers to the language. "Fighting", here is an adverb that modifies "spends" because it tells how Ben spends. It is not a verb. The sentence breaks down like this: SUBJECT: Ben VERB: spends DIRECT OBJECT: rest (of the holiday) ADVERB PHRASE that modifies the verb: fighting (lots of monsters from outer space) Notice that "fighting" has no subject. Present participles can have objects ("monsters") but they NEVER have a subject. That is why they do not have the capacity act like verbs. They come from verbs ("to fight") but they themselves are not verbs. Their "parents" are verbs but they have chosen not to follow in their parents' footsteps! In the last sentence, "to fight" is an infinitive, not a verb. Everything I said about participles applies to infinitives as well. An infinitive is the NAME of a verb, but it cannot act as a verb. It can have an object, but cannot have a subject. The last sentence breaks down like this: SUBJECT: he VERB: has DIRECT OBJECT: time ADJECTIVE PHRASE that modifies the direct object: "to fight with his cousin".

“To fight someone” and “to fight with someone” have different meanings. The first is serious. Usually it has a figurative meaning but here it doesn’t. Most people don’t have to fight aliens. I fought the insurance company for three years in order to get paid. He’s been fighting alcoholism his whole life. How many villains has Batman fought? ‘Fight with’ describes the types of conflict that occur between people who have a relationship. Brothers often fight with each other. He fights with his wife over the stupidest things. Teenagers almost always go through a phase when they fight with their parents. Don’t worry too much about it.