Halliday & Matthiessen (1999: 86):
… in the overall meaning base, lexically construed folk and scientific taxonomies do not start at the highest degree of generality in delicacy; they are ordered in delicacy after those systems that are construed grammatically. For example, while ‘plant’ is the “unique beginner” of a particular folk taxonomy, there are several steps in the construal of things that are more general than this — steps that are constructed in the grammar, in categories such as ‘thing’, ‘conscious/non-conscious thing’, ‘countable/non-countable thing’ and the like.