Samuel Kirkham, English Grammar in Familiar Lectures
“ As a verb in the indicative mood is converted into the subjunctive when it is preceded by a conjunction expressing doubt, contingency, supposition, &c., so a verb in the potential mood, may, in like manner, be turned into the subjunctive; as, "If I could deceive him, I should abhor it; Though he should increase in wealth, he would not be charitable." ”
