'Had I known, I would have called you.' No 'if' anywhere — yet this is a full third-conditional sentence. In formal and literary English, 'if' can be dropped entirely when the clause starts with had, were, or should, and the auxiliary inverts to the front instead: 'If I had known' becomes 'Had I known'; 'If I were you' becomes 'Were I you'; 'If you should need help' becomes 'Should you need help.'

Today also reviews mixed conditionals — combining two different timeframes in one sentence, common in real fluent speech: 'If I had studied medicine, I would be a doctor now' (past condition, present result). 🔊