What kind of reasons do we give for things happening? In physics, we call the reasons causes and the things that happen are called effects. One way that these causes can be divided into two is by distinguishing between chances and necessities: causes that can happen and those that must happen. In contrast, in describing reasons why we as agents do things, we merely call the reasons reasons, or reasons for actions. One way these reasons can be divided into two is by distinguishing between choices and plans: the reasons for making a choice and the explanations for planning a goal.
If we cannot understand the reasons that something happened, we might claim that it was just random or it was just fate. We might come to believe that there is an agent we know that is responsible for the thing happening by either a choice they have made or a goal they have planned. Or we might even think that there is an agent or institution hidden from our knowledge that might be responsible, with hidden choices and plans. This is not the same as the world operating by chance and necessity.
If we cannot understand the reasons why an agent does what they do, their behavior appears random or even insane. If we can understand the reasons for their actions, their behavior may be justified to us, but it can still be considered good or bad. Of course, our good actions may be ineffectual against the world’s chances and necessities, in which case we are not responsible for outcomes. Even so, our bad actions and our plans and goals may still be scrutinized in a normative way. If an agent’s actions or plans appear to be contrary to our goals or society’s goals, that agent is at odds with us or society.
Ordinarily what is called free will consists of the freedom to make choices and plans and to attempt to carry them out. What is free will free from? Is it free from physical laws, or the energy and matter of our brains and bodies? That doesn’t make much sense to me. Is it the same as chance? That isn’t a freedom worth wanting, as Daniel Dennett says. If we do something that doesn’t make sense to us, various experiments have determined that we then construct reasons for ourselves that we can understand and believe that explain our actions. Are they the real reasons or have we just lied to ourselves?
Regardless whether free will exists, the explanations given by choices and plans are required for our understanding of each other’s actions and goals. 
However, these must not be confused with the chances and necessities of the world when and where they apply.
Notes:
This four-fold consisting of Choice, Chance, Fate, and Plan is inspired by the Modal Verbs: May, Can, Must, and Should. One might consider it as the double duality of internal or external and possibility or necessity.
Also consider changing “chance” to “luck”, and “choice” to “pick”.
Links:
http://en.wikipedia.org/wiki/Causality_(physics)
http://people.wku.edu/jan.garrett/302/4persona.htm
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A rose I give to you
All fours are fantastic, but especially this superhero team! I hear that a reboot of the movie franchise is on the way.
Equivalent Exchange 