Sentience was the ability of a species to think intelligently. It was commonly determined by the being's ability to reason, speak, and manipulate tools. Creatures that completely lacked that ability were classified as non-sentient, while those that appeared to have emerging sentience were classified as semi-sentient. Droids, despite not being technically alive to begin with, were regarded as sentients.
According to The Essential Guide to Alien Species, ghostwritten by Ann Margaret Lewis based on data collected by Senior Anthropologist Mammon Hoole, "a species given the sentient definition is considered able to reason and understand abstract metaphorical concepts and ideas, make and use tools, and communicate with written or spoken language." Species that did not reason at all and survived via their natural instincts were classified as non-sentient, or sometimes as sub-sentient. Non-sentience did not imply the lack of any form of intelligence. Species that appeared to have emerging sentience were classified as semi-sentient. These included species that had very primitive capabilities to manipulate tools, use language, and/or solve problems. Examples included the Arkanian dragon, the Zillo Beast, the Bafforr tree, the wampa, pecoppi parrots, and the sarlacc.
A group of sentient species
In the waning years of the Galactic Republic, an Annual Mid-Rim Domesticated Sub-Sentient Show was held for non-sentient creatures.
The Galactic Empire would often recategorize sentient species such as the Wookiees as non-sentient, allowing it to enslave them without formally violating the laws protecting sentient beings from such abuse.
In Star Wars Legends, sentience encompasses both sentience and sapience in the real-world.