Synthesis and antithesis are two elements of a dialectic argument, the third being the original thesis. The difference between synthesis and antithesis is that antithesis is an idea in opposition to another, while a synthesis blends two opposing ideas together. Antithesis is likely to occur when a thesis is put forward, but synthesis is not guaranteed to happen unless both protagonists decide to compromise or someone decides to compromise for them.
One similarity between synthesis and antithesis is that neither can exist without a thesis to work from. Their relationship to the central thesis defines the differences between them. A thesis can be proposed in a letter, article or speech and sets out an idea and elaborates on it with examples and reason. The aim is to get readers and listeners to agree with the idea.
An example of a thesis came from St. Augustine of Hippo, a Roman theologian, who set out the idea of original sin. He believed that all babies were born sinful and would go to hell unless baptized. Even after baptism, all humans are still sinful without divine aid from God. He believed predestination and not good works decided if someone went to heaven or not.
The antithesis is a counter position to the thesis. It is set out in the same way in a speech or in written form and also attempts to persuade people to agree with it instead of the thesis. Pelagius, a British priest, proposed a counter idea to Augustine’s ideas on original sin. Pelagius believed that babies were born innocent and man could earn a place in heaven if he or she did good works and lived a good life.
One big difference between synthesis and antithesis is that while an antithesis is common in reaction to a thesis, the production of synthesis is not. Synthesis attempts to find common ground between two arguments. It insinuates that both the proponent of the thesis and the champion of the antithesis are willing to discuss the matter and reach a conclusion. This can be done by a third person or by the creators of the thesis and antithesis together.
Often this is not the case. With Augustine and Pelagius, neither, especially Augustine, was willing to compromise. The Church then ruled on the matter and found in favor of Augustine. This led to Pelagius being denounced as a heretic and hounded for the rest of his life. The Church ruled that there could be no synthesis and antithesis, just the thesis.
Once basic points of agreement are found, the synthesis then attempts to reconcile other elements of the thesis and antithesis. If the Catholic Church had forced Augustine and Pelagius to sit down and compromise, they would have formed a synthesis together. Pelagius might have agreed that man is sinful, but Augustine would have relented on babies, allowing an un-baptized baby to go to heaven and not hell.