Psychology is the study of mind and behavior. The human mind became central to 20th century thought.
Sigmund Freud is considered one of the most prominent thinkers of the first half of the 20th century. In his book Civilization and its Discontents, Freud makes mention of individual development (urge towards happiness + urge towards union with others) and civilization development (creating unity out of individuals). Freud states that these types of development oppose one another. This imbalance between the individual and the community of which Freud makes mention is quite different from Adam Smith’s ideas about the same topic. Adam Smith talks of people being driven by self-interest. As each individual becomes the best he/she can at their respective skill, it leads to the betterment of the society (civilization) as a whole.
In the same book, Freud discusses two of the drivers of human life: men being inclined to aggression and sexuality. Freud states, "If private property were abolished, all wealth held in common, and everyone allowed to share in the enjoyment of it, ill-will and hostility would disappear among men." I disagree with that statement. If you get rid of those those things, there would be an increase in moral hazard among members of society. (Moral hazard, in business, is the risk that one party to a transaction will engage in behavior that is undesirable from the other party's point of view.) There would be an increased number of people who would either stop working and mooooch off of everyone else OR people would be much more frivolous in there dealings with others because there is no fear of losing a home or personal belongings since all are equal.
Carl Jung was another influential psychiatrist of the 20th century.
A few quotes of his that I really liked were:
"The more a man's life is shaped by the collective norm, the greater is his individual immorality." ("Psychological Types", 1921) AND
"Without freedom there can be no morality." ("Relations between Ego and Unconscious", 1928).
I like these quotes because I feel that they are applicable to the world we live in today. Sex, drugs, and immorality are becoming more and more accept mainstream among members of society today. You could even say that being involved in such acts has become "normal". However,when we are chaste and moral, we become truly free and able to act and make decisions for ourselves. It is when we abstain from the use of drugs, alcohol, immorality and obey God's commandments that we become free.