337. Use the subjunctive mood in contrary to fact conditions.
Wrong. If I was you, I should not do that.
Right. If I were you, I should not do that.
Revise. If he was not ill, he might win today.
338. Use have, the correct auxiliary, not of, carelessly written for the unaccented have.
Wrong. You should of seen him run.
Right. You should have seen him run.
Revise. If it had not rained today, we might of gone away.
339. Had ought and hadn’t ought are not standard English; ought has no past participle and no past perfect tense.
Wrong. You hadn’t ought to have come so soon.