As the Bible’s Book of Numbers tells the story (at 13:17ff), Moses sends out one man from each of the twelve tribes of Israel, with instructions to “go and spy the land” of Canaan. Caleb returns with the favourable news that Canaan is ripe for the taking; the others report that its fortified cities and strong population make it an impossible target. The Israelites decide not to invade the land. As a result, they incur the wrath of God and condemn themselves to wandering in the desert for 40 years—in possibly one of the earliest and most spectacular intelligence failures “on record.”Ever since Moses, espionage has been an enduring tool of statecraft. As John Le Carré’s iconic character George Smiley vividly tells it, Why spy? . . . For as long as rogues become leaders, we shall spy. For as long as there are bullies and liars and madmen in the world, we shall spy. For as long as nations compete, and politicians deceive, and tyrants launch conquests, and consumers need resources, and the homeless look for land, and the hungry for food, and the rich for excess, your chosen profession is perfectly secure, I can assure you.The Secret PilgrimSmiley’s description of the world of intelligence is not exactly a ringing endorsement of Le Carré’s own early career as a spy. Smiley and his creator are correct, of course, that governments—and private corporations—shall always spy. In fact, espionage is, at least sometimes, the morally right thing to do—more strongly still, it is a moral duty. This might seem controversial. Yet, the military strategist and general Sun Tzu offers an unambiguously moral defence of espionage in his classic treatise The Art of War (6 BC). War is so costly to the sovereign’s soldiers and subjects, particularly his poorest subjects, that the sovereign is under an obligation to try and shorten it by acquiring knowledge of the enemy’s intentions and dispositions. Given that the only way. . .