Cells are, in shorthand, the smallest definable unit of 'magic' that can be still parsed as a spell. The trick boils down to semantics and understanding at what point does a [sentence] lose potency/ semantic meaning, or otherwise loses the impact of 'intent'. See, I think it boils down to whether or not Will/ Intent *is* the catalyst (what triggers a casting) OR if Will/ Intent within itself can be the casting- basically what is the scope of impact of Mental within a practitioners praxis.
My Father taught me primarily Will-driven workings so I am biased towards the belief that Intent can be the casting within itself. This doesn't really have broader implications on Earth-dependent castings, moreso astral and spirit metaphysics; still, it speaks towards internal direction. I cast outwards, and I hold no division between 'myself' and my surroundings.