In a book where humans' alien attackers are actually referred to as "the Others," it seems like a safe bet that Other-ness will somehow figure into its themes. The interesting thing about the Others in The 5th Wave is that their Other-ness is a source of both comfort and intense anxiety for humans.
Part of what makes the Others so scary is that they seem unknowable; for a long time, no one even knows what the aliens look like, much less what they want. Eventually, Cassie and the others find out the Others look just like humans, which is distressing on a lot of levels. For one thing, it makes things confusing. (You never know who you're fighting…or kissing.) For another, it's hard to stomach that humans and aliens have anything in common.
The Others seem unusually cruel and spiteful towards humans. Their mission isn't just about claiming planet Earth.
The Others need Earth for the survival of their species. They don't have any sort of personal grudge against humans.
The Others are into mind games like whoa. First they disguise themselves as humans, which allows them to secretly infiltrate (and eventually take over) important military bases. Then they train child soldiers to kill their fellow humans through another series of deceptions. That's a pretty neat party trick, don't you think?
Evan is an alien, so it's not exactly a surprise that he's into deception. (His seems to be for a good cause, though—he just wants to keep Cassie safe.) It's also worth noting that the other two main characters, Cassie and Zombie (who are both humans), each pose as someone they're not at least once in the book. Cassie acts like a young child so she can infiltrate the military base and save her brother, and Zombie dresses up like a doctor in his own attempt to save Sammy.
Cassie sees through Evan's deception almost right away. She didn't buy his act, but she couldn't face it until he stated it in no uncertain terms.
Cassie truly believes that Evan is human up until the point that he admits he's an alien. She had doubts, but he lied so well that she was able to put them aside.
Have you ever noticed that, when it comes to the end of the world, survivors tend to be persistent sons of guns? Whether it's The Walking Dead or The Road, fictional apocalypse tends to bring out humans' will to persevere against adversity. And The 5th Wave is no different.
Interestingly, Cassie and Zombie have the same goal: to save Sammy. (Saving the world is too tall of an order.) Separately, but in parallel, they keep pushing to make it happen even when everyone around them says it's impossible. Ultimately, despite major struggles, they both come to Sammy's rescue.
The question is: what happens after that? Sure, they saved Sammy, but can the human race survive? This is just the first book in the series, so we don't know the answer yet.
The 5th Wave is a novel in which persistence pays off.
The three main characters don't fight to stay alive for their own sakes. They persevere because of their dedication to other people.
In a book about the end of the world, you can expect to see a lot of death. This particular alien apocalypse has wiped out more than seven billion people, which is almost everyone. Almost.
The scale of that tragedy is no joke, and its impact is taken very seriously in The 5th Wave. At the same time, the story flirts with the idea that all this death is really nothing new. Sure, it's unusual and sad and terrible that everyone's dying at once. But at the end of the day, weren't all those people going to die anyway? That's what happens when you're human. The Others didn't invent mortality.
Cassie and Ben come to that realization separately, and it's interesting to watch them process it. When Ben contemplates his inevitable death, he feels defeated. Cassie, on the other hand, seems to draw strength from it. If she's going to die either way, what does she really have to lose?
In The 5th Wave, knowing you're going to die is source of despair. It means that nothing really matters.
In The 5th Wave, knowing you're going to die is a source of empowerment. It means you have nothing to lose.
From tectonic plates to the circle of life, things on Earth are always changing. That's nothing new. Still, when seven billion people croak in just a few months' time, a lot of practical—and emotional—adjustments that must be made.
There's the big stuff, like no more electricity or cars. There's the little things, like no more cold drinks. Then there's the utter terror of watching almost everyone around you die badly. Cassie, Ben, and the other humans in The 5th Wave are dealing with a lot of strain on a lot of levels, and each person has their own way of coping.
Also, some people choose not to cope at all. We're told that, after the alien attacks, many people killed themselves, unable to find a way to deal with all that upheaval.
Through the characters of Cassie and Ben, The 5th Wave suggests that change is a force for bad.
Through the character of Evan, The 5th Wave suggests that change can be a force for good.
Fear of murderous alien colonizers would be enough to make your mind play tricks on you. That said, these particular murderous alien colonziers are really, really into playing with people's minds. For that reason, it's a little hard differentiate between run-of-the-mill crazy people and the Sherlocks who've managed to crack the case about Camp Haven being headed up by aliens posing as military personnel.
With the constant threat of "going Dorothy"—that's military speak for losing your mind—looming over all the characters in The 5th Wave, they have to stay on their toes. Whenever someone has an insight, they have to ask themselves: am I in fact brilliant? Or am I just cracking under pressure? It's hard to know the difference, which suits the Others just fine.
In the upside-down world of The 5th Wave, sane is the new crazy, and crazy is the new sane.
In The 5th Wave, the Others try to make humans crazy—not so much to kill them as to torture them.
The Others are waging a war against the human race, and so far the humans have had a hard time fighting back. You'll notice that the struggles of characters like Cassie and Ben aren't anything so grand as saving the world; their goal is to save just one little boy.
In The 5th Wave, at least, they're playing defense, not offense.
The Others have some impressive weapons—including tsunamis and killer plagues—up their sleeves. Arguably, their most effective tactic is the way in which they keep humans guessing about what will happen next. Another is the way in which they sow doubt in people's hearts about who's actually human. (The Others look like regular people.) Finally, there's the child army they're training back at the alien military base, Camp Haven. What's up with that, anyway? Like the humans in the book, we can only speculate.
Pop culture's representation of alien attacks has left Cassie and her fellow humans totally unprepared for the real deal.
Pop culture provides plenty of clues about alien tactics that Cassie and the gang have missed. Maybe they just haven't watched the right movies.
Identities in The 5th Wave are super-unstable. The human characters, especially Cassie and Ben, feel disconnected from the happy high school students they were before the attacks. On the alien front, the Others look just like humans, so it's hard to discern who's who. Plus, Evan switches sides, going from Cassie's hunter to her protector in a matter of moments.
As the humans struggle to figure out who they can trust, we readers experience a similar feeling. The author drops a lot of hints about Evan's alien identity, but we don't know for sure until he admits it to Cassie. We watch Vosch murder Cassie's dad, but he provides a semi-believable excuse for that behavior later in the novel.
The point is, identities in The 5th Wave aren't set in stone. They're always subject to change—which can be good or bad.
War changes who you are, whether you want it to or not.
Cassie and Ben think that the war has changed who they are to the core, but we can see that many of their most essential personality traits seem to be intact.