What is the old lie in the poem "Dulce et Decorum Est?"

The lie Wilfred Owen refers to is the Latin sentence that comes at the very end of the poem: Dulce et decorum est pro patria mori. Translated into English, this sentence means "How sweet and fitting (or glorious) it is to die for one's country!" Owen calls it old because it is a line from an ode by Horace, a Roman poet who lived and wrote in the first century B.C. In Horace's poem, the sentence is presented at face value, not with irony; Owen objects to its sentiment.

In his poem named after the Latin saying, Owen shows how the men who died fighting for Britain in World War I did not die a "sweet" death. He describes the death of a soldier who could not get his gas mask on in time and was overcome by chlorine gas. His death was anything but "sweet." Descriptions like "guttering, choking, drowning," and "hear the blood come gargling from the froth-corrupted lungs, obscene as cancer, bitter as the cud of vile incurable sores on innocent tongues" portray the reality of trench warfare in all its lack of glory.

The other "lie" Owen refers to, by comparison, is the lie that recruiters and the culture at large told to young men to get them to sign up to fight in the Great War. He equates the jingoistic war poetry of his time with the sentence by Horace. Originally Owen intended to title this poem "To Jessie Pope." Referred to as "you" and "my friend" in the poem, she was one of the writers who pumped out vacuous jingles meant to inspire enlistment. One of Jessie Pope's many poems of this type is "Who's for the Game?" The poem asks, "Who would much rather come back with a crutch / Than lie low and be out of the fun?" Calling the war "fun" was exactly the type of "lie" that Owen was exposing in his poem.