“When the rookery is pretty well filled, and the nest-building is in full swing, the birds have a busy and anxious time. To get enough of suitable small stones is a matter of difficulty, and may involve long journeys for each single stone. The temptation is too strong for some of them, and they become habitual thieves. The majority remain stupidly honest. Amusing complications result. The bearing of the thief clearly shows that he knows he is doing wrong. He has a conscience, at least a human conscience, i. e., the fear of being found out. Very different is the furtive look of the thief, long after he is out of danger of pursuit, from the expression of the honest penguin coming home with a hard-earned stone. “An honest one was bringing stones from a long distance. Each stone was removed by a thief as soon as the owner’s back was turned. The honest one looked greatly troubled as he found that his heap didn’t grow, but he seemed incapable of suspecting the cause. “A thief, sitting on his own nest, was stealing from an adjacent nest, whose honest owner was also at home, but looking unsuspectingly in another direction. Casually he turned his head and caught the thief in the act. The thief dropped the stone and pretended to be busy picking up an infinitesimal crumb from the neutral ground.” “The Heart of the Antarctic,” SIR ERNEST SHACKLETON, Vol. II, p. 253 (Section on the Adelie Penguin, by James Murray, Biologist of the Expedition). The word “conscience” was perhaps originally synonymous with consciousness, but it gradually came to mean _self_-consciousness of a very special type, namely, the silent commendation or censure which a man may bestow upon his actions or his projects. This word “conscience” replaced the Middle English term _inwit_,—a term made famous in the title of a book (circa 1340) called the “Ayenbite of Inwit” (that is, the “Again-bite or Remorse of Conscience”). The concept of conscience has played an important part in modern ethical theory, and it is supposed by many persons to be the foundation of all morality. What place it deserves to hold in a constructive, mechanistic ethics can be determined, however, only by careful analysis. So many extravagant claims have been advanced in its behalf as to make one suspect that none of them are true. Things which people have “always heard lauded and never discussed” are only with difficulty saved from oblivion when intellectual revolutions have altered the emphasis which man puts on the values of life. It was thus with the word “soul,” and with the word “immortality,” and it is likely to be the same with the word “conscience.” At least it will be an advantage to look at the philosophical pedigree of this once mighty shibboleth.