Radionica engleski 7. u 22

Why “have welcomed”, but not “has welcomed”?
In book "Agents of Empire: Knights, Corsairs, Jesuits and Spies in the Sixteenth-Century Mediterranean World" Written by Noel Malcolm, there is this sentence:
Sultan Suleyman the Magnificent was apparently spoiling for a fight with Venice, and may even have welcomed an incident in early 1537 when a hot-headed Venetian naval commander, Alessandro Conferini, attacked three Ottoman ships and sank two of them, the really giving Suleyman a pretext for war.
My question is: Why author, British-English native, write "have welcomed", but no "has welcomed".
Response:
Apparently, you don't see that the whole verb in the sentence is may have welcomed. We usually use an infinitive after modal verbs. May is a modal verb and "have welcomed" is a perfect infinitive.

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