I've written a lot about subspace and have often been asked to describe it. I tend to view it as a state of mind rather than as the result of physical play as it is often portrayed (usually by writings that assume every submissive is a masochist).
In my past analysis of subspace I often viewed it as a priority shift from an inward stance (what I want) to an outward stance (what can I do for her?) in a sub's mental state that is often tied to psychological and sexual triggers. While this may describe what I end up feeling as I progress into deeper stages of subspace, it tends to skip a few of the earlier stages.
Tonight I was thinking about how to describe it in a way that covers all stages. What seemed to make sense to me is that in any stage, subspace is a (progressive) state of wanting more but being willing to accept less.
In its shallowest states, a sub may crave sexual contact and fetish presence but rather than simply jerking off themselves, they relinquish control of those factors over to the Domme. Basically, they get horny and have an increased desire for kink and sexual attention but accept a less immediate form of gratification.
This seems to hold true for most stages of subspace as well as most fetish activities. E.g. A sub in chastity and deep subspace may dearly want to cum but instead accepts teasing and the idea of "maybe next time." This in turn deepens their subspace and makes them crave the orgasm even more, which is what makes the disappointment of further denial so exhilarating. A sub in an extremely deep state (bordering on slave level state) may deeply crave attention, love, praise, etc. but may simply accept not being punished as a reward for good service.
As states deepen, the number and strength of desires may grow while the sub is willing to accept progressively less of their immediate desires. Note: By immediate desires I am referring to desires in the moment and not desires we rationalize while outside of subspace.
I may think about this definition a bit more. Does anyone have any thoughts on this?