The Culture is a symbiotic society of artificial intelligences (AIs) (Minds and drones) and humanoids who all share equal status. As mentioned above, all essential work is performed (as far as possible) by non-sentient devices, freeing sentients to do only things that they enjoy (administrative work requiring sentience is undertaken by the AIs using a bare fraction of their mental power, or by people who take on the work out of free choice). As such, the Culture is also a post-scarcity society, where technological advances ensure that no one lacks any material goods or services. As a consequence, the Culture has no need of economic constructs such as money (as is apparent when it deals with civilizations in which money is still important).
Marain is the Culture's shared language. Designed by early Minds, the Culture believes (or perhaps has proved, or else actively made true) the Sapir–Whorf hypothesis that language influences thought, and Marain was designed to exploit this effect, while also "appealing to poets, pedants, engineers and programmers". Designed to be represented either in binary or symbol-written form, Marain is also regarded as an aesthetically pleasing language by the Culture. The symbols of the Marain alphabet can be displayed in three-by-three grids of binary (yes/no, black/white) dots and thus correspond to nine-bit wide binary numbers.
Related comments are made by the narrator in The Player of Games regarding gender-specific pronouns, and by general reflection on the fact that Marain places much less structural emphasis on (or even lacks) concepts like possession and ownership, dominance and submission, and especially aggression. Many of these concepts would in fact be somewhat theoretical to the usual Culture citizen.
Marain itself is also open to encryption and dialect specific implementations for different parts of the Culture. M1 is basic Nonary Marain, the three-by-three grid. All Culture citizens can communicate in this variant. Other variants include M8 through M16, which are encrypted by various degrees, and are typically used by the Contact Section. Higher level encryptions exist, the highest of these being M32. M32 and lower level encrypted signals are the province of Special Circumstances. Use of M32 is reserved for extremely secret and reserved information and communication within Special Circumstances. That said, M32 has an air of notoriety in the Culture, and in the thoughts of most may best be articulated as "the Unbreakable, Inviolable, Holy of Holies Special Circumstances M32" as described by prospective SC agent Ulver Seich. Ships and Minds also have a slightly distasteful view of SC procedure associated with M32, one Ship Mind going so far as to object to the standard SC attitude of "Full scale, stark raving M32 don't-talk-about-this-or-we'll-pull-your-plugs-out-baby paranoia" on the use of the encryption (Excession).
There are no laws as such in the Culture. Social norms are enforced by convention (personal reputation, 'good manners' and by, as described in The Player of Games, possible ostracism for more serious crimes). Minds generally refrain from using their all-seeing capabilities to influence people's reputations, though they are not necessarily themselves above judging people based on such observations, as described in Excession. Minds also judge each other, with one of the more relevant criteria being the quality of their treatment of sentients in their care. Hub Minds for example are generally nominated from well-regarded GSV (the largest class of ships) Minds, and then upgraded to care for the billions living on the artificial habitats.
The only serious prohibitions that seem to exist are against harming sentient beings, or forcing them into undertaking any act (another concept that seems unnatural to and is, in fact, almost unheard of by almost all Culture citizens). As mentioned in The Player of Games, the Culture does have the occasional "crime of passion" (as described by an Azadian) and the punishment was to be "slap-droned", or to have a drone assigned to follow the offender and "make sure they don't do it again".
While the enforcement in theory could lead to a Big Brother-style surveillance society, in practice social convention among the Minds prohibits them from watching, or interfering in, citizens' lives unless requested, or unless they perceive severe risk. The practice of reading a sentient's mind without permission (something the Culture is technologically easily capable of) is also strictly taboo, and Minds that do so are considered deviant and shunned by other Minds (see GCU Grey Area). At one point it is said that if the Culture actually had written laws, the sanctity of one's own thoughts against the intrusion of others would be the first on the books.
This gives some measure of privacy and protection; though the very nature of Culture society would, strictly speaking, make keeping secrets irrelevant: most of them would be considered neither shameful nor criminal. It does allow the Minds in particular to scheme amongst themselves in a very efficient manner, and occasionally withhold information.
It has been argued within the novels by opponents of the Culture that the role of humans in the Culture is nothing more than that of pets, or parasites on Culture Minds, and that they can have nothing genuinely useful to contribute to a society where science is close to omniscient about the physical universe, where every ailment has been cured, and where every thought can be read. Many of the Culture novels in fact contain characters (from within or without the Culture) wondering how far-reaching the Minds' dominance of the Culture is, and how much of the democratic process within it might in fact be a sham: subtly but very powerfully influenced by the Minds in much the same ways Contact and Special Circumstances influence other societies. Also, except for some mentions about a vote over the Idiran?-Culture War, and the existence of a very small number of 'Referrers' (humans of especially acute reasoning), few biological entities are ever described as being involved in any high-level decisions.
On the other hand, the Culture can be seen as fundamentally hedonistic (one of the main objectives for any being, including Minds, is to have fun) rather than to be 'useful'. Also, Minds are constructed, by convention, to care for and value human beings. While a General Contact Unit (GCU) does not strictly need a crew (and could construct artificial avatars when it did), a real human crew adds richness to its existence, and offers distraction during otherwise dull periods. In Consider Phlebas it is noted that Minds still find humans fascinating, especially their odd ability to sometimes achieve similarly advanced reasoning as their much more complex machine brains.
To a large degree, the freedoms enjoyed by humans in the Culture are only available because Minds choose to provide them. Nevertheless, social convention within the community of Minds seem to make it impossible, as well as abhorrent, that these freedoms should be curtailed in a society that cares about the happiness of its members. The freedoms include the ability to leave the Culture when desired, often forming new associated but separate societies with Culture ships and Minds, most notably the Zetetic Elench and the ultra-pacifist and non-interventionist Peace Faction?.