1839 Oliver Beale Peirce: "The grammar of the English Language. What is a Principal asserter? It is one which, of itself, conveys the idea of the existence, action, or influence of some person or thing denoted by the word on which it depends for sense; as I am; I love; William writes; George studies. What is an Auxiliary asserter? It is one which, of itself, does not convey the idea of existence, action, or influence of the subject of remark; but is joined to a principal to vary its meaning, and forms, with the principal, but one asserter; as, I shall love. William has written. George will study.
Source: wiktionary