This is a new text considering the arguments that are most commonly used to claim that nonhuman animals are not sentient, and the reasons to reject those arguments. This paper complements the others that you may find at our website section about animal sentience, which explains what are the criteria to infer that a being is sentient, which beings are likely to be sentient and what the problem of consciousness is, among other issues.
Most of us believe and act on the assumption that other humans are conscious based on their observable behavior. There are also other criteria for consciousness, such as relevant physiology and evolutionary logic, that humans satisfy. However, not only humans, but many nonhuman animals satisfy these criteria. Due to this, consistency, as well as plausibility and simplicity lead us to conclude that a large number of them are conscious.
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The text also includes links to other texts addressing other aspects of this issue.