Halliday & Matthiessen (2014: 249):
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e.g. Heliotropic plants must know where the sun is.
Which particular creatures we choose to endow with consciousness when we talk about them may vary according to who we are, what we are doing or how we are feeling at the time; different registers show different preferences. Pets, domestic animals and other higher animals are often treated as conscious; the owner says of the cat she doesn’t like milk, whereas someone who is not a cat lover, or who has been annoyed by that particular specimen, is more likely to refer to the animal as it. But any entity, animate or not, can be treated as conscious; and since mental process clauses have this property, that only something that is being credited with consciousness can function in them as the one who feels, thinks, wants or perceives, one only has to put something into that role in order to turn it into a conscious being.
Blogger Comment:
e.g. Heliotropic plants must know where the sun is.