Everything and nothing is conscious: default assumptions in science and ethics

Historically, scientists and philosophers have tended to assume that animals lack consciousness until evidence shows otherwise. Recently, however, some researchers have proposed reversing this assumption. Other options are available as well; for example, in addition to assuming that all animals are conscious, we can assume that all living beings are conscious, that all beings with nervous systems are conscious, that all beings with complex cognition are conscious, or even that all beings are conscious. I examine these options from scientific and ethical perspectives, showing that different default assumptions can be appropriate for different purposes and in different contexts. I also suggest that a default assumption of consciousness may often be best for both science and ethics.