Free will and determinism both represent overly strong claims when applied in an unqualified way. I’ve already written a bit about the evils of voluntarism.
Aristotle’s “cause” or aitia can be any kind of reason why something is the way it is, and a way that something is typically has multiple reasons of different kinds. The modern notion of cause, by contrast, is intended to provide a single, complete explanation of why an event does or does not occur. The modern notion, unlike the Aristotelian one, is univocal. (See also Equivocal Determination.)
In the reception of Aristotle, historically too much attention was paid to the identity of the underlying “something”, as contrasted to the way something is, emphasized by Aristotle himself — to the point where the standard Latin translation for ousia (Aristotle’s main word for a way of being) came to be substantia or “substance” (something standing under). By contrast, the central books of Aristotle’s Metaphysics start from the notion of something persisting through a change and ask what that is, but in addressing that question eventually reverse the order of explanation, and argue that what can best be said to be underlying just is a way that something is actively what it is. An ousia may be expressed in speech as a simple noun, but this is only a kind of shorthand that can always be unpacked into something like an adverbial expression.
In general, Aristotle suggests that we should value ends more than origins. How something turns out is much more important than where it came from.
Already in Neoplatonism, there was a decidedly non-Aristotelian turn toward putting higher value on origins than results, based on the idea that the One was the origin of everything, and nobler than everything. For monotheistic theologians, it was obvious that God as origin was superior to creation.
Aristotle ends up suggesting that what he calls efficient causes — the direct means by which change is triggered or effectuated, which would include mechanical cases like the classic bumping billiard balls — are not what is most fundamental in making things the way they are. By contrast, the Latin medievals made the efficient cause the root of all others, also applying it to God’s activity of creation from nothing.
Common early modern notions of causality started from this medieval reversal of Aristotle, assuming that efficient causes of the billiard-ball variety came first in the order of explanation. This was related to a widespread anti-Aristotelian privileging of immediacy. Kant and Hegel later developed strong critiques of the privileging of immediacy, but this aspect of their thought was not adequately understood and highlighted until recently. A reduction of all causes to allegedly immediate causes is an error common to both voluntarism and determinism.
Descartes developed a bottom-up explanatory model, starting from simple mechanical causes. This was good for science at a certain stage of development, but bad for philosophy. I would not wish to say that bottom-up explanations have no use (in delimited contexts, they most certainly do). I mean only that it is a delusion to think that nothing else is required, or that they can provide an absolute starting point.
In ethics, Aristotle’s notion of character is a nice relief from the seesaw of free will and determinism. Character is an acquired disposition to act in certain ways. The character of an individual resembles the culture of a community, and the same word (ethos) is used for both. We acquire it gradually over time, from an accumulation of our actions and things that have happened to us. Due to the contributing role of our actions in successive layers of character formation, we are in a broad way accountable for our disposition. On the other hand, it makes little sense to blame someone for acting in accordance with their disposition.