If I had studied medicine, I would be a doctor (C1 Grammar)

A mixed conditional joins two different times. For a past action whose result reaches into now, use if + had + the past participle, then would + the base verb: If I had studied medicine, I would be a doctor. To make it negative, use hadn't in the if-half and wouldn't in the result: If I hadn't left, I wouldn't be so tired now. For a question, move would to the front: Would you be a doctor if you had studied medicine? The if-half sits in the past; the result sits in the present.

A past action with a result that still holds

• If I had studied medicine, I would be a doctor.
• If she had accepted the offer, she would live in Haffenville.
• If they hadn't sold the flat, they would own it today.
• Would he be fluent now if he had moved abroad?
• Not "If I had studied medicine, I would have been a doctor (right now)." — say "If I had studied medicine, I would be a doctor.". When the result is still true today, the result-half is would + base verb, not would have + past participle — would have been wrongly seals the result off in the past.
• Try it: Years ago, Lars decided not to learn to drive. Because of that single past decision, he still relies on buses for his daily commute. Which one fits a past choice whose result still holds? (If he had learned to drive, he would be far more independent. / If he had learned to drive, he would have been far more independent.) Answer: If he had learned to drive, he would be far more independent. — The past choice still shapes his daily life, so the result reaches into the present: would be far more independent. "Would have been" would seal the result off in the past, but the effect on him carries right through to today, so the result-half stays in the present.

A lasting trait with a result in the past

Run it the other way for a lasting trait that shaped a past event: use if + were, then would have + the past participle: If I were more patient, I would have waited. Note the were — this formal if-half uses were for every subject (I, he, she, it). You will also hear and read was here ('if I was more patient'), and it is not an error, but were is the form formal writing and exams expect, so it is the one to produce. Make it negative with weren't and wouldn't have: If she weren't so cautious, she wouldn't have turned it down. For a question, move would to the front: Would she have waited if she were more patient? The if-half describes how someone generally is; the result sits in the past.

• If I were more patient, I would have waited for the results.
• If she were bolder, she would have applied last year.
• If he weren't so disorganized, he wouldn't have missed the deadline.
• Would they have stayed if they were happier here?
• Not "If I had been more patient, I would have waited." — say "If I were more patient, I would have waited.". For a trait you still have, the if-half uses were. Had been patient points at one passing moment instead of the lasting trait that shaped the past choice. (In the were slot, was is also heard; were is the formal choice.)
• Try it: Mei is a cautious person, and she has always been that way. That lasting caution is the reason she turned down a risky promotion last spring. Which one fits a lasting trait that changed a past event? (If she were bolder, she would have accepted the promotion. / If she had been bolder, she would have accepted the promotion.) Answer: If she were bolder, she would have accepted the promotion. — Her caution is a lasting trait she still has, so the if-half uses the subjunctive present form: If she were bolder. "Had been bolder" would point at one passing moment of boldness, but the sentence is about who she generally is, and that shaped a past choice.

The formal version: drop "if" and invert

In formal or literary English you can drop "if" and invert instead. Put had before the subject for the past-time half (Had she accepted the offer, she would live here), or were before the subject for a present trait (Were he more patient, he would have waited). For a negative, keep not after the subject: Had I not left, I would still be there. The meaning is exactly the same as the "if"-version — only the register changes. It sounds more formal and emphatic, so reach for it in essays, speeches, and polished writing, and keep the plain "if"-version for everyday speech.

• Had I studied medicine, I would be a doctor.
• Were she bolder, she would have applied last year.
• Had they not sold the flat, they would own it today.
• Were I in charge, things would have gone differently.
• Not "If had she accepted the offer, she would live here." — say "Had she accepted the offer, she would live here.". Inversion replaces "if" — drop "if" and move had (or were) in front of the subject. Never keep both "if" and the inversion.
• Try it: ____, he would be far more independent now. Build the formal, "if"-dropped version of the if-half. Situation: years ago he never learned to drive, and that single past choice still limits him today. Answer: Had he learned to drive — Drop "if" and put had before the subject: Had he learned to drive, using the past participle learned. "If" is wrong because the inversion replaces it — you never keep both. "Would have learned" belongs in a result-half, not the if-half, and "did" has no place in a conditional if-clause. The result stays in the present — he would be far more independent now — because that past choice still limits him today.
• Try it: A past action with a result that still holds: they never bought a home, so they are tenants to this day. A lasting trait with a past result: Diego is naturally careful, which is why he declined a risky deal years ago. Match each one. Which way does each run? Answer: A past action with a result that still holds: they never bought a home, so they are tenants to this day. → 1 → If they had bought a home, they would own one. · 2 → If he were bolder, he would have taken the deal. A lasting trait with a past result: Diego is naturally careful, which is why he declined a risky deal years ago. → 1 → If they were richer, they would have bought one. · 2 → If he had been bolder, he would take risky deals. — A past action with a result that still holds runs had + would: had bought, would own one. A lasting trait with a past result runs the subjunctive past form + would have: were bolder, would have taken the deal. Read which time the cause sits in and which time the result lands in — the second option runs both the wrong way round.