Copied from my own blog: http://surprisinglycomplex.blogspot.fi/2013/05/bakemonogatari-behind-summer-triangle.html
Warning! This Blogpost contains some profanity, horrible grammar and will make you s*it brix.
Bakemonogatari is usually noted for it's unusual art style, enjoyable soundtrack and surprisingly deep characters. Yes, words philosophy and symbolism are words that are often put there, but they're almost never followed up on. Why is that? Does the subject matter actually make it harder to explain the philosophical content of the show? I don't know, but enough rambling, time to start pouring some heavy text.
Bakemonogatari, in it's heart, is a character study. This, while easy to say, is not actually that easy to understand. Think about these questions for a sec:
-Why are there no other people in the whole world than Araragi and the girls (Senjougahara's father not counted)?
-Why do objects (Cars, bicycles and houses) not connected to Araragi all look exactly the same?
-Why are violent and sexual themes often so gratuitous?
During the first 2 questions some will think about budget restraints or it just being the artstyle, but if it is artstyle, WHY? On the other hand, the third question may be thought as some kind of fanservice-y thing so they would have something to show in the trailers or such, but from my point of view, that is not the case. As you can guess, it has something to do with the thing "character study." You are absolutely right.
Being a character study, what IS is not important, but what Araragi FEELS there is, is. This may sound like some pseudo-philosophical bullshit, but bear me a sec, I'll explain. It's rather easy. The whole series is actually more in his head than in his surroundings, it's just shown from a different camera angle. Why is Araragi's bike different from the rest? Because it is HIS, and is thus special for him, he pays attention to it. Paying attention is the key here. He doesn't pay attention to the surrounding people (Except Senjougahara, Hanekawa etc.) thus they "don't exist." It also explains the extreme nature of violent and sexual scenes.
Why are the fight scenes always so weird and abstract, usually having weird colours and over the top effects? Because that's what Araragi feels to be in the fight. IT HURTS. A LOT. And thus he overestimates the effects of pain and it is seen by the viewer as a huge pool of blood and gore. Notice how the surreal nature and colours of ie. the fight between the Rainy Devil disappears IMMEDIATELY the red scene accompanied with Senjougahara's line appears. That's how. He puts his attention to something else (Senjougahara) thus the chaos of the fight has ended. Surprisingly simple.
Same happens with sexual things. He's a teenager. It's not just fanservice. He's a teenager. So every little perverted thing may be HUGE in the mind of such libido-minded guy like Araragi, making the scenes themselves more perverted intentionally. It may even be, that some things that characters are doing are not actually even executed, it's just Araragi's mind doing all the work.
Ok, that's some warmup, now we're talking romance. (HEAVY SPOILERS!! SKIP IF YOU HAVEN'T WATCHED IT!)
Back to the character study. We can extend this theory so far, that it can make about half of the whole series kind of pointless. As everything, absolutely everything is basically in Araragi's head. That itself, the series being what Araragi believes it to be, is breaking the fourth wall. How? It is said in the series, that the very essence of Oddities is that they are what people believe them to be. This is lampshadowed as Oshino points out, that Shinobu has become childish because Araragi believes she is just a child. The whole series is what Araragi believes it to be. That is why some things, for example seem to happen but don't happen. As an example take the very beginning of the series, where Araragi is running up circular stairs in his school, and Senjougahara falls to his hands. Later, we see Araragi running down the stairs of the school, that are NOT circular. The staircase never was circular. It was always normal. And Senjougahara didn't fall from far, she probably just tripped from top of some stairs. Araragi just thinks that scene with circular stairs and 50-meter fall, because he felt that Senjougahara FELL TO HIS HANDS.
We can extend this with the point that I made some time ago. Like sexual things that may not even exist out of Araragi's mind, many other things in the series may not. Like for example, the many times Araragi is threatened by Senjougahara with sharp object can be just taken as interpretation of a different situation, like a one where she says something where the wrong answer would ruin him mentally, but we're just shown it in a physical form.
TL;DR?
We see what Araragi sees, mentally more than physically.