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Sentience is the capacity to be affected positively or negatively. It is the capacity to have experiences. It is not the mere capacity to perceive stimuli or react to some action, as in the case of a machine that performs certain functions when we press a button. Sentience, or the ability to feel, is something different, namely the ability to receive and react to such stimuli... Read more

Close up of caterpillar climbing on branches

To be conscious is to be able to have some kind of subjective experience or awareness of something.1 We can only experience something if we are conscious, and if we are conscious it means we can have experiences. Conscious creatures can experience something external in the environment or something internal to the body. It can be the experience of a feeling or of a thought of any... Read more

Sheep family sleeps together in the grass

There are three general criteria for deciding whether a being is sentient. These involve considerations that are (1) behavioral, (2) evolutionary, and (3) physiological.   Behavior When we experience suffering or enjoyment, we tend to behave in certain ways. We grimace, we cry, we groan... And the same is true of other sentient beings. This applies to both human beings... Read more

Three parrots groom each other in the grass

Animal sentience studies look at nonhuman animals’ ability to have positive and negative experiences. At the most basic level, positive and negative experiences are pain and pleasure, but they can also include psychological states of suffering and joy. Where there is sentience there must also be consciousness. This is because sentience, the ability to feel pleasure and pain,... Read more


As explained in the page on the problem of consciousness, consciousness can be defined as the state of having experiences. Conscious states, or mental states, are situations in which one is having any kind of experience, be it a sensorial experience, a thought, an emotion or whatever. Self-consciousness, a particular form of consciousness, is a broad term that is used to mean... Read more

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Given the criteria we have for considering whether a being is conscious, it is reasonable to conclude that vertebrates and a large number of invertebrates are conscious. The clearer cases are those of animals who have a centralized nervous system whose central organ (basically, a brain) has some development. However, there are a number of animals who possess centralized nervous... Read more

sea-sponge-what beings-are-not conscious

Beings that have no centralized nervous systems are not sentient. This includes bacteria, archaea, protists, fungi, plants and certain animals. There is the possibility that a number of animals with very simple centralized nervous systems are not sentient either, but this is an open question and cannot be settled yet. The reasons that lead to this conclusion are as... Read more


If we accept that certain behaviors in humans are indicators of suffering, then evolutionary logic tells us that these same behaviors in nonhuman animals show us that they are suffering. For example, we can often tell an animal is suffering from the way they cry out, whimper, writhe, or start favoring an injured body part. Over longer time periods, injury and chronic pain are... Read more

Two deers touch noses in the snow

The section on animal sentience presents several compelling arguments all of which conclude that many nonhuman animals are sentient. In addition, Animal interests shows why the interests of sentient nonhuman animals cannot be considered to have less weight than humans’ interests. Implicit in both conclusions is the further conclusion that being sentient is morally important. The... Read more

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