Note 117 — DISSERTATION IV.
Reading edition
A similar use of the verb occurs after wish; "I wish I had my estate now in possession;" this would be expressed in Latin. Utinam me habere, using the present of the infinitive, or Utinam ut haberem; but this Imperfect tense of the Subjunctive, both in Latin and French, is used to convey the same ideas as English verbs after if; if I had, si haberem, si j'aurois, and whatever may be the name annexed to this form of the verb, it cannot, in the foregoing sense, have any reference to past time.
The common phrases, I had rather, he had better, are said to be a corruption of I would rather, he would better, rapidly pronounced, I'd rather. I am not satisfied that this is a just account of their origin; would will not supply the place of had in all cases. At any rate, the phrases have become good English.