Two topics that have affected artists since the Greeks have been ethos and pathos.
In the great age of Greek philosophy and theater, 600 BC to approximately 300 BC or later, Greek thinkers suggested that pathos, the feeling and transmission of emotion, was integral to human existence and health. Evidence of this emerges in sculpture near the end of the Archaic period, by 550 BC. It can be seen in works such as The Dying Warrior from the pediment of the temple of Aphaia at Aegina.
It would not be enough to merely recognize the mimetic or naturalistic qualities of a human figure, we must stop and contemplate the subject's feelings and thoughts. In such a way, we may be examining our own thoughts and feelings, a process Aristotle called catharsis.
This introduced an ethic for artists. Is an artist obligated to capture a viewer's attention and excite emotions?
One ethic all artists recognize is craftsmanship. There should be an integrity to the use of materials and the stylistic approach to creation.
Breugel felt an ethic to preach to his Protestant contemporaries. Thus he placed the New Testament Bible story of The Massacre of the Innocents into his own village and his own contemporaneous times, thus forcing his viewers to experience empathy and sympathy.
Salvador Dali had attacked the projection of meaning into tropes in Surrealist art, but after a meeting with Sigmund Freud in New York during 1938, Dali painted The Temptation of St. Anthony in which he used his Surrealist painting style to affirm symbolic meaning and reference the religious topics of sin, guilt and temptation. This resulted in Dali being kicked out of the Surrealist Congress, yet he continued to paint such religious paintings as St. John the Divine and The Dark Night of the Soul and The Last Supper.
Photojournalism probably began in the Crimean War while photographic technology was still in its infancy. Many photographers tried to communicate pathos by the time LIFE magazine debuted in 1936 and cemented the picture story as a narrative device for news. Dorothea Lange was a photographer for the U.S. government when she documented the plight of migrant farm workers during The Dust Bowl following The Great Depression. How do you tell "the heart" of a story in a compelling way when people's hearts have already been wrung dry for a decade? She did it by finding a Madonna in the dust.
Franco's fascists were impatient to win the Spanish Civil War in 1936, so they escalated the attacks by bombing a historic mountain town symbolic of The Old Republic, Guernica. Lacking a war machine of their own, the fascists appealed to Mussolini who appealed to his allies the Nazis. Nazi Stuka dive bombers tested their firepower during the night on the defenseless Guernica. Pablo Picasso, a Spaniard expatriated as a Cubist in Paris, used the mythic icons of Cubism to convey the horror, heart and history of the event as a monument, a memorial, something art has been used for throughout human history. In that way primitive means speak to primal emotions.