Sapience

"Write me a creature that thinks as well as a man, but not like a man."

- John W. Campbell

Sapience refers to the capacity to think and comprehend the world in an elaborated way, and to possess an elaborate sense of self-awareness as well as an elaborate capacity for reasoning and abstracting. It sets intelligent beings apart from non-sapient machines, vegetation and wildlife. In many ethical systems, it grants an individual the right to be treated as a person.

In science fiction, there has been a long and unfortunate tradition to erroneously employ the word "sentient" instead of "sapient" to refer to such beings. In reality, sentience means the capacity to feel and experience sensations, which is something most animal life possesses. Therefore, many life forms that have been referred to in fiction as "non-sentient" are actually clearly sentient, and merely non-sapient.

Additionally, the word "sophont" has been coined by Karen Anderson and adopted by other authors as an alternate synonym for "sapient".

Definition
Ancient Greek philosopher Aristotle classified man as the only rational animal, claiming that the ability to make rational (and not purely instinctive) decisions sets man apart from the other species, which he labelled as irrational. This same distinction between rational and irrational animals was also adopted by other Greek and Roman scholars.

Today, it's generally accepted that most animal species (or at least most tetrapods) possess this ability to some degree, as they can demonstrate the capacity to learn and find creative solutions to problems based on knowledge that is not instinctive. The intelligence and self-awareness displayed by many real life animal species to some degree has demonstrated that there is an entire spectrum of sapience levels.

Classification
In speculative biology and fiction, as in real life, the line between sapient and non-sapient is extremely subjective. For simplicity, however, we can adopt a system with three main categories for classification.
 * Non-sapient life forms are more likely to act upon instinct than acquired knowledge. They're often capable of learning, but they cannot display higher levels of thinking and questioning. If they operate in a society, their culture will probably be limited. Metacognition (i.e. "thinking about thinking") is still beyond them. Sapient races might domesticate them and employ them to perform certain tasks, but they will not be treated as equals. In real life, most animal species would fall under this category.
 * Semi-sapient life forms are as likely to act upon instinct as upon acquired knowledge. They can easily operate in groups and display higher levels of culture and even metacognition, but are still not fully capable to operate as a person in a sapient society. Therefore, they're usually still treated as "wildlife", legally. In real life, many species of great apes, birds, elephants and cetaceans could potentially fall under this category.
 * Sapient life forms are less likely to act upon instinct than upon acquired knowledge. They typically exhibit higher levels of culture and metacognition. In principle, they should be fully capable to operate as a person in society and are deemed legally-responsible for their acts (at least upon reaching adulthood). In real life, humans are the only known species universally recognized as falling into this category.

It should be noted that the definitions above are still extremely simplistic and subjective, and may not apply easily to some species. Determining whether a behavior is instinctive or not can be a difficult task, as is determining whether an individual life form is fit to comprehend the legal responsibilities and rights that are generally bestowed upon those regarded as sapient.

Hypothetically, an alien life form may be as intelligent as a human being, operate in cities and produce all sorts of technology while still being incapable of comprehending our own laws and customs.

Variable sapience
Sometimes, a species in fiction will have variable sapience levels, depending on a number of factors.
 * Age: some species start life as non-sapient and only achieve sapience later on. Laiderplacker offspring are feral, and Chirpsithra have described their children as "voracious". In species which undergo metamorphosis, it's more common for the larval form to be non-sapient whereas the adult form is sapient, but the reverse can also be true, e.g. in Flutterbies, the larval form is the sapient one.
 * Caste: in species which operate in hives, it's possible that some castes are sapient and others aren't. In Tractator hives, only the Gravis is sapient, all other individuals are just mindless drones. Likewise, Selenites have varying levels of sapience, depending on their social roles and functions.
 * Hive mind: many species regarded as superorganisms operate as a single mind. Therefore, the individual components of said mind might not be sapient when isolated from it. The Ibs are colonial creatures in which one component, the "pod", constitutes the brain, whereas the other components cannot think. The Giant Polyp is only intelligent when its individual cells come together. The Barrel-beasts seem to operate as one organism with no regard for individuality, seeing as individuals will have no qualms about sacrificing themselves to be recycled as nutrients for the colony. Individual Telfi; although capable of surviving outside their colonies; barely retain their sapience when isolated.
 * Sex: there exist some species with sexual dimorphism in which one sex is sapient and the other isn't. In the Kzinti and Thrintun, the female form is non-sapient. In the Chirpsithra and Cygnans, it's heavily implied that the male form is non-sapient, and the same is true of the Temptors.
 * Assimilation: some alien species have the ability to absorb the minds of life forms they have preyed upon. If the victim was a sapient being, the predator, even if initially non-sapient, may acquire sapience as a result, as can be the case with Alzabo or Coalescent Organisms. Alternatively, non-sapient hosts might behave as sapient if their minds are controlled by a sapient parasite or external force (e.g. Zarbi drones under the control of the Animus).
 * Transformation: although natural shapeshifters usually retain their minds intact regardless of their form, there exist some creatures which may alternate from sapient to non-sapient during their transformation. This often happens to sapient creatures afflicted with some form of therianthropy. Moon Beasts and many kinds of Lycanthropes are examples of this.
 * Environmental factors: the unnamed insectoids from "Love is the Plan the Plan is Death" are only sapient during the warm seasons of their home planet's translation cycle. During the winter season, they lose all their thinking abilities and start operating on pure instinct.

Culture and society
The behaviors and habits of sapient life are as varied as possible, as the universe has demonstrated that sapience can emerge in all kinds of life forms, including predators, prey, parasites, symbionts, vegetables, fungi, algae, microbes, viruses, minerals, obelisks, machines, color shades, memetic lifeforms, space-borne spheres of dark matter, living nebulae and living worlds.

Alien races might be as peaceful as the Clangers or as genocidal as the Daleks. Some might be as far above us on the evolutionary scale as we are above the amoeba. And yet, others might not.

Because of this tremendous variety of alien minds, it isn't surprising that not all sapients behave in a comprehensible manner to us. Some, like the Mi-Go have often been deemed incomprehensible in their actions. In some cases, like that of the Barrel-beasts, it's not even possible to determine whether they are indeed sapient or not. The Martians fail to recognize Humans as sapient. So might be the case of the Crystalline Entity, which Captain Jean-Luc Picard suggests might be sapient, but incapable of recognizing humanoids as such. In another similar instance, establishing proper communication with the Ocean of Solaris has been proven impossible.

The majority of sapient species have been observed to be social and to dominate the use of technology, which often results in said species altering their environment to suit their needs, by means of agriculture, urbanization and so on. Even so, not all sapient species are technology-users, and some have been observed to live in perfect harmony with nature, such as the Alflololians and the Pahvans. Some sapients, such as the Atheleni, are physically incapable of using tools, since they lack any organ of manipulation such as hands or tentacles.

Regardless of the above, it is possible that the most characteristic feature of sapient life is its desire to fulfill its own potentials in some way, to not only perpetuate its existence but to give meaning to it. And yet, not even that is universal, as the entirely apathetic Lotophagus Veneris are sapient, but possess no desires of any kind.