"Within the S/M subculture, different people use the words 'submissive' and 'slave' to mean many different things. When submissives say 'I want to be your slave,' sometimes they mean only that they want to be tied up and whipped. Many professional dominants routinely refer to their (usually not very genuinely submissive clients) as 'slaves.' At the other extreme, there are people who want to be full-time personal servants, and who truly want to exist solely for their Dom(me)'s use, pleasure, and convenience. And there are many shades in between these two extremes."
THE OUTRIGHT NON-SUBMISSIVE MASOCHIST or KINKY SENSUALIST. Not into servitude, humiliation or giving up control; just pain and/or spiced-up sensuality, on the masochist's own terms and for the masochist's own direct pleasure (i.e. turned on solely/mainly by one's own bodily sensations rather than by being "used" to gratify one's partner's sadism).
PSEUDO-SUBMISSIVE NON-SLAVE. Not into even playing "slave," but into other "submissive" role-playing, e.g. schoolteacher scenes, infantilism, "forced" transvestism. Usually into humiliation, but NOT into servitude, even in play. Dictates the scene to a large degree.
PSEUDO-SUBMISSIVE PLAY SLAVE. Likes to play at being a slave; likes to feel subservient; may in some cases like to feel one is being "used" to gratify partner's sadism; may even really serve the dominant in some ways, but only on the "slave's" own terms. Dictates the scene to a large degree; often fetishistic (e.g. foot worshipers).
TRUE SUBMISSIVE NON-SLAVE. Really gives up control (only temporarily and within agreed-upon limits), but gets her/his main satisfaction from aspects of submission other than serving or being used by the dominant. Usually turned on by suspense, vulnerability, and/or giving up responsibility. Doesn't dictate the scene except in very general terms, but still seek mainly her/his own direct pleasure (rather than getting one's pleasure mainly from pleasing the dominant).
TRUE SUBMISSIVE PLAY SLAVE. Really gives up control (though only temporarily; only during brief "scenes" and within limits) and gets main satisfaction from serving/being used by dominant, but only for FUN purposes, usually erotic. May not be into pain. If so, is turned on by pain indirectly, i.e. enjoys being the object of one's partner's sadism, on which the submissive places very few requirements or restrictions.
UNCOMMITTED SHORT-TERM BUT MORE THAN PLAY SEMI-SLAVE. Really gives up control (usually within limits); wants to serve and be used by the dominant; wants to provide practical/nonerotic as well as fun/erotic services; but only when the "slave" is in the mood. May even act as a full-time slave for, say, several days at a time, but is free to quit at any time (or at the end of the agreed-upon several days). May or may not have a long-term relationship with one's Mistress, but, either way, the "slave" has the final say over when she will serve.
PART-TIME CONSENSUAL-BUT REAL SLAVE. Has an ongoing commitment to an owner/slave relationship and regards oneself as the property of the dominant at all times. Wants to obey and please dom(me) in all aspects of life-practical/nonerotic and fun/erotic. Devotes most of the time to other commitments (e.g. job) but Dom(me) has first pick of the slave's free time.
FULL-TIME LIVE IN CONSENSUAL SLAVE. Within no more than a few broad limits/requirements, the slave regards herself/himself as existing solely for the Dom(me)'s pleasure/well being. Slave in turn expects to be regarded as a prized possession. Not much different from the situation of the traditional housewife, except that within the S/M world the slave's position is more likely to be fully consensual, especially if the slave is male. Within the S/M world, a full time "slave" arrangement is entered into with an explicit awareness of the magnitude carefully, with more awareness of the magnitude of power that is being given up, and hence is usually entered into much more carefully, with more awareness of the possible dangers, and with much clearer and more specific agreements than usually precede the traditional marriage.
CONSENSUAL TOTAL SLAVE WITH NO LIMITS. A common fantasy ideal that probably doesn't exist in real life (except in authoritarian religious cults and other situations where the "consent" is induced by brainwashing and/or social or economic pressures and hence isn't fully consensual). A few S/M purists will insist that you aren't really a slave unless you're willing to do absolutely anything for your Dom(me), with no limits at all. I've met a few people who claimed to be no-limit slaves, but in all cases, I have reason to doubt the claim.
The above list isn't intended as a rigid classification. Most submissives don't fall neatly into one of these categories; there are still further shades in between. (For example, a live-in slave with an outside paying job would be category 7 1/2. Also the same submissive may attain different degrees of submission with different Dom(me)s. The list is intended simply to show the wide range of different possible meanings of the words "submissive" and "slave."
In the S/M subculture, the majority of "submissives" seek scenes in categories 1-3, whereas most of the Dom(mes) I know (including myself) seek slaves in categories 6-7. If you're a submissive in categories 1-3, you are probably best off seeking a relationship not with a Dom(me) but with a fellow "sub," or with a switchable person into both roles. The two can take turns acting out each other's "submissive" or masochistic fantasies.
When a submissive tells a dominant, "I want to be your slave," it is often hard to tell exactly what is meant. Lots of people fantasize about a much greater degree of submission than they are able or willing to attain in real life, and lots of "slaves," especially inexperienced ones, overestimate their own desire for real-life servitude. A dominant must carefully find out how far the "slave" really wants to go.
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