<span>The First Caliph, Abu Bakr (632-634 A.C.) <span>The Second Caliph, 'Umar (634-644 A.C.) </span><span>The Third Caliph, Uthman (644-656 A.C.) </span><span>The Fourth Caliph, Ali (656-661 A.C.) </span></span><span>
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History language and english culture
Francis Bacon was the first to formalize the concept of a true scientific method.