Inversion after a fronted adverb
CEFR C1
The passé simple: for reading, not speakingRecognising passé simple forms when reading and knowing which infinitive they belong to…Cleft sentences: c'est… qui, ce qui… c'estHighlighting an element with c'est… qui, c'est… que and the ce qui / ce que / ce dont…Connectors for formal argumentUsing the connectors that carry a French argumentative text, and telling them apart from…The imperfect subjunctive, for readingRecognising the forms when reading and knowing which spoken tense they match, without…The impersonal constructions of formal FrenchOpening the sentence with impersonal il and giving each phrase its preposition and mood.Accents and the cedillaPlacing é, è, ê and ç correctly, and knowing that in French an accent changes the sound…The rule, in three lines
When certain adverbs open the sentence, the subject moves after the verb: «Peut-être viendra-t-il», «Ainsi a-t-il décidé», «À peine était-il sorti que…». If the verb ends in a vowel, a linking -t- is inserted: viendra-t-il.
The usual slip. Fronting the adverb and leaving the order alone, or reading the inversion as a question because of the hyphen and the verb-first order.
Why it catches you out. English does exactly the same thing —Hardly had he left…, Never have I seen…— so you already own the idea. What is new is the linking -t-, which has no English counterpart and is easy to leave out.