It's commonly held among kinky folk that bottoms of all genders outnumber tops by some non-trivial percentage. Among talented tops I have known there is a propensity, however veiled sometimes, to need to switch occasionally. I have no opinion on the continuing debate over "true" topping and "true" bottoming, but it's fair to observe that there's at least some fuzziness in the margins regarding labels, and that they may in fact have little bearing on the actual structure of the power within an exchange.
Exchange. Now there's an interesting word. I expect this post will receive some carefully considered comments for my suggestion of the following, but within an honest scene dynamic power is not so much exchanged as it flows along a gradient. The term "power exchange" is to me at best inaccurate and slightly disingenuous, like a psychic condom to set people's minds at ease about what's really transpiring between them, and at worst irresponsible in potentially destructive ways. Real harm to the popular perception of BDSM is done when bromides such as "power exchange" are proffered to vanilla folk, which in the short term may defuse their untutored discomfort somewhat, but it only advances their ignorance and in the end, like "plausible deniability," can only be viewed as spin, a result I personally would just as soon avoid.
Where tops and bottoms are fulfilling their potentials then there is scant potential for any back flow of power - in the words of William Burroughs (in an interview with filmmaker Shirley Clark) everyone can be a god: "And how do you get to be a god? By doing your job and doing it well." I'm in favor of participants and lovers knowing and loving their jobs, doing them, and keeping their practice up so they can do those jobs well (loving one's job is, of course, not the same as doing it well).
I think the power that a bottom offers to a scene is a priori in the form of consent, and during in the form of expression. Such expression (although one hopes it registers with the top) is less directed at the top or anyone in particular than it is let loose in the world for the delectation and delight of anyone who should happen upon it (usually just the top). Make no mistake, I mean in no way here that a bottom's expression of power is less than that of the top's, quite the opposite - it can be huge. I mean that bottom energy en scene is diffuse in nature as opposed to directed. Think about it. Bottom energy is broadly available, even through photography. Rare is the top whose energy extends beyond his or her partner, or is capturable in a lens. The experience of the bottom is justly the focus of most scene portrayals because the energy of the bottom is in its nature available. All sorts of power lights up scene space like stellar energy, but in their unique characteristics we can note distinguishing energetic features that clearly identify top and bottom. Top = directed, focused, bottom = diffuse, available.
Does good topping entail bottoming, or at least having had the experience of bottoming? This is often offered as an article of BDSM faith and there is much empirical evidence to support the supposition, but that people are capable of or like to switch is, I believe, neither necessary nor sufficient to explain high-quality topping. The energy of a person that emerges as good topping takes the form of a chain reaction and is self perpetuating; an apt metaphor could be said to be the sun. The sun makes no request of the earth in order to direct toward it energy in what appears to the earth to be perfectly parallel rays (i.e., focused). From the earth's perspective this energy is uniquely directed and the earth makes much of it, including what I would say is the apogee of its expressive capacity, life. The earth also reflects a small percentage of the sun's energy back and outward (exactly 0.39 of it in fact, known as the earth's albedo), but mostly the sun's energy is absorbed and used to profound effect, one might even say god-like effect.
That the sun's energy flow is emergent and unilateral enhances the metaphor for topping in that any top whose energy is derivative (i.e., non-emergent) is, in effect, a functionary, a tool, if you will, and perhaps a dangerous one. I would go as far as to submit that what anyone who derives their mandate for visiting suffering on another from any source other than within themselves (including from a bottom) is not topping. While it is completely possible for bottoms to top from the bottom, this is neither an exchange nor a gradient. It is a closed system, and as such is probably subject to the equalizing force of entropy wherein energy and its potentials dissipate - we've all been in scenes where this has happened and I leave it to the reader to form a judgment about such episodes.
Within the commingling of energies between top and bottom lies the potential for spectacle and magic and transcendence about which I've written frequently in this forum. I know I don't much like the feeling of energy passed through to me by powers removed from my experience, and I'm happy to have had only light dealings with such feeling, enough to know of its creepiness. Advances in consciousness and experience can naught but come of authenticity, so one has to ask what the value of transacting any power in a BDSM frame would be if any part of the energies involved were not authentically those of the participants.
That the exercise of derivative power has dangerous potentials is easily exemplified by rise of the Nazis in Germany or the actions of the outgoing administration in Washington, but perhaps more concisely so by a study well known to practicing sadists everywhere - Stanley Milgram's Obedience to Authority. 45 years on, Jerry Berger of UC Santa Clara has replicated Milgram's experiment with only minor updatings and observed in so doing that people are not much less likely to visit lethal suffering on innocent strangers than they were before it became popular in the last generation or so to question authority. The results (to be published in American Psychologist), while not quite falling within a statistical margin of error, were near duplicates of Milgram's from 1963. Apparently over 70% of people will torture a stranger to death if told to do so by someone they perceive to be in authority.
That's what I'm talking about. That's derivative power. Its flow is unilateral and along a gradient, but it is not emergent within the person charged with its exercise. It is, therefore, dangerous precisely because its exercise is diffused and not directed. It is economic, and therefore not intimate. It seems almost superfluous to note that a person who merely passes energy through to a recipient is not a top because they cannot be held responsible for having originated the actions resulting in the suffering, and yet that is what is implied by a power exchange.
While I believe firmly that both parties are responsible in the execution of an SM tableau, each is responsible within their domain. As a facile example, once a bottom is physically restrained the buck for both parties' physical well-being stops at the top. As a firm believer in government by and for the people, I brook little in the way of abuse by entities whom I have empowered by right of enfranchisement, but it is a western conceit that a veneer of democratic principle be applied to all situations wherein any power is in evidence. In scene space a top is charged with the consent of the governed to govern, and the form such governance takes is in that moment an enlightened despotism, as impolitic as that may seem. If BDSM were at its core merely the tarting-up of egalitarian commonplaces, I daresay it would not be half so challenging or erotic.
In a true democracy power lies with the people and the people are responsible for their poor choices, and for the shabbiness of their elected officials. In scene space, the bottom is rightly held responsible for entering into the arrangement even if it is open-ended (my favorite kind), but once that line is crossed power emerges from and resides with the top. To have it "given" by the bottom (as pretty as that looks) or derived from anywhere or anyone else is, as Milgram shows and Berger reinforces, a recipe for irresponsible behavior and quite possibly real harm.
Once again, with thanks to Dave Annis.