"Classes" of Spellcasters

Remember: The Weave exists adjacent to every point in space and is separated from our world by a barrier, when the barrier is breached potential energy pours forth into our world and usually becomes progressively more "specific" in it's form (physical characteristics, function, or both), and spellcasters are kin who are able to both create breaches and manipulate the transformation of this energy in such a way as to create "magic".
Sentience tends to be associated with a discrete body (i.e., a conscious entity usually inhabits a single, separable, corporeal form as opposed to having no form or inhabiting multiple forms), but the physical characteristics of objects in-and-of-themselves are not sufficient to describe the sentience. As an example, a rock can be sentient (i.e., an earth elemental) and another rock can be unsentient, and there may be absolutely no physical difference between these two rocks whatsoever. 
Intuitively we know that there is more to life and sentience than simply the body. Most scholars break down the non-physical components of a single sentience into the mind (the part of us that handles computation and memory and often corresponds strongly to central nervous systems) and the spirit or soul (a part of our sentience that persists after death, likely existed prior to birth in some form, determines our connection to things beyond and greater than ourselves, and affects the unfolding of the mind over a creature's lifespan in a way that is still very poorly understood). It can be helpful, as well, to divide the mind into the conscious and the unconscious. After all, the mind is not a unitary entity. Colloquial phrases such a "she was at war with herself", "part of him wanted do it, part of him didn't", and "they couldn't control themself" hint at an underlying truth: while a part of our minds is under our singular control and volition, we have inumerable drives, emotions, states, and factors beyond our control that impact it's functioning. The unconscious mind is, unsurprisingly, poorly understood, but recent research out of the Verdant Academy supports the theory that it is strongly associated with what we casually call force of personality or charisma.
Wizards and Arteficiers: Intelligence and the Consious Mind Most spellcasting (the wild magic of some sorcerers being the most common exception) requires conscious effort to both breach the barrier to the Weave and to shape the resulting surge of energy. What makes wizards different is that they rely purely on their conscious efforts; considerable study, memorization, theorization, and practice have led them to a point where they understand the Weave enough to know how to "untangle" it - if only minorly and briefly - creating their breach. They then use these same theorums, movements, sounds, and calculations to influence the energy they gain.
Druids, Rangers, and Witches: Wisdom and the Spirit
Sorcerers and Paladins: Charisma and the Unconscious Mind
Clerics and Warlocks: Borrowing Breaches
Bards:

Type

Metaphysical, Arcane