Hello, Brian:
1) "... the author (sg.) and their (pl.) opinion."
One man cannot be both singular and plural.
This is nonsense.
2) No degree as a grammarian. But I have read many Ph.Ds that did not use proper grammar. So then, a college degree does not indicate anything except willing submission to brainwashing of some sort.
My accomplishments, assisted by the Spirit of God, are to comprehend written messages that no one else that I have encountered, in 20 years of research, has been able to comprehend.
A short list is:
The 7 Spirits of God - Isa 11.1-4; Eph 4.4-6; Rev 5.12; Rev 7.12.
3 Ages of Man - 2Pet 3.6, 3.7-10, 3.13.
3 General Resurrections - 1cor 15.22-24.
3 Days in the Tomb - Mt 12.40.
6 Particular Resurrections - Enoch, Elijah, the Lamb of God, Old Heavens, First Resurrection, New Heavens.
3) "A theologian should always double check his sources."
Now, this proves that your previous statement was wrong.
"Theologian" and "his" are both singular.
Previously you wrote, "author and their opinions."
This is a terrible mistake.
You have really touched on one of the critical points of Bible translation and interpretation.
The singular should be considered separate from the plural.
Keep plugging.
hoaryhead