Nietzsche is particularly harsh on our conception of "free will." First, he argues that the will is far more complicated than we make it out to be: the word "I" obscures and fudges together a whole complex of commanding and obeying wills. This "freedom" of the will comes only from identifying this "I" as the source both of the commanding and the obeying. The concept of free will also relies on the erroneous notions of cause and effect, which see our will as a "cause." Cause and effect are a part of a larger picture of physics, according to which nature is governed by laws. Nietzsche argues that this is a democrat's interpretation of nature: we could equally well see it as totally lawless, governed only by the unfettered assertion of wills.
Nietzsche's understanding of "truth" is subtle and deep. Logically speaking, "true" and "false" apply to sentences and propositions, not to things or wills or people. Any statement that purports to be true can be seen as expressing a particular point of view. According to Nietzsche, no point of view can comprehend absolute truth: there are only different perspectives from which one can see a matter. If one sees a matter from only one perspective, one is seeing a distorted and incomplete picture. Truth, being something expressible only in propositions, demands a point of view, a particular perspective, and, in claiming truth for that perspective, distorts the bigger picture. Truth, we might say, falsifies the overall picture. Once we abandon a belief in absolute truths and absolute falsehoods, the relationship between truth and falsity becomes richer and more complex.
Our "truths," according to Nietzsche, are not absolute, but are rather particular interpretations of what we see. For instance, Nietzsche argues that it is only "true" that nature operates according to laws if we take a particularly democratic perspective toward the workings of nature. Nietzsche sees the same regularity in nature, but doesn't interpret this regularity as the proper governance of law so much as the constancy of the domination of stronger wills over weaker ones. Nietzsche's discussion of wills will be discussed shortly.
Our interpretation of experience is ultimately based on the perspective we choose, and the perspective we choose is largely based on moral assumptions and prejudices: we see the world the way we want to see it. Philosophers are in the business of trying to justify seeing the world in their own particular way, and they come up with reasons why the world should be viewed from their perspective rather than some other. Ultimately, they see their moral prejudices and their perspective on things as "truths." As a result, philosophy is as much autobiography as anything else: philosophers attempt to justify and to convince others of what it is that drives and motivates them.
The obvious, and sometimes justified, objection to lots of talk about relative truths and perspectives and the like is: "But aren't there some things that are simply true or simply false? That 1 + 1 = 2 doesn't depend on my perspective." True enough. To understand what Nietzsche means, we need to understand his conception of the will to power.
According to Nietzsche, the significant fact about the universe is that it is always changing. A philosophy of facts and things only reinforces the misconception that the universe is fixed. Nietzsche identifies will as the agent of all change in the universe, and so focuses his philosophy more on the will. All wills struggle for domination, independence, and power over one another, which is the source of change in the universe. This change is thus effected by what Nietzsche calls the "will to power," the struggle for independence and dominance over other wills. Nietzsche sees people not as "things" or "selves" but as a complex of wills, all struggling with one another for domination. He calls philosophy the "most spiritual will to power" because it is an attempt on the part of the philosopher to impose his prejudices and assumptions--his "spirit"--on everyone else. The philosopher wants his will to be "truth."