Weber does not start his discussion with a definition of what he means by the spirit of capitalism. Rather, he presents examples of what he means by this spirit (most notably through the writings of Benjamin Franklin), and through these examples he draws out what the relevant traits of this spirit are. He then appeals to his audience's own experiences, saying that this attitude does indeed permeate modern capitalistic society. Overall, this approach is convincing. Franklin's writings do seem to suggest the attitudes Weber attributes to him, and this characterization does seem to correspond with modern capitalism. However, it is worth noting that Weber's analysis of Franklin has been criticized as inaccurate. If true, this puts a great strain on the validity of Weber's thesis, since much of his argument rests on this exposition. There are other techniques that Weber could have used. He could have done a broad survey of diaries or other personal narratives to see if common attitudes emerged. He could have looked to the books people read as clues to their values. He could have looked at the laws that were passed and debates that were had to see the values that were expressed. He also could have taken a more quantitative approach; critics notice that he had very few numerical surveys in his study. It is up to the reader to decide which approach is most appropriate. Since Weber's study is largely historical in nature, he is limited by the available literature and cannot rely on interviews or random surveys. Weber also could have defined the capitalistic spirit at the very beginning. This might have been clearer than defining it through examples. However, his point in not doing this is that he is not trying to look for the emergence of some arbitrarily defined phenomenon. Rather, he is interested in something that is rooted in reality, and he wants to define it through reality.

The doctrine of predestination holds that God has predetermined which humans are saved and which are damned. Nothing done on earth, including good works and participation in the sacraments, can change one's fate. This doctrine was held by the Calvinists, and by other ascetic Protestants. According to Weber, this doctrine was inwardly consistent, and therefore rational. If God is truly all-powerful, nothing people could do on earth should be able to change his commands. Therefore, predestination puts man's fate back into God's hands. Weber believed that this doctrine had a major psychological impact. Followers felt a profound inward loneliness. Each person had to face a fate he could not control, and his Church and community could not help him. The individual became obsessed with finding signs about his own salvation; he craved proof. As a result, he threw himself into his work, seeing worldly success as a sign of God's grace. Furthermore, he reacted angrily to others' sins and failings. Rather than feeling pity about human weakness, he saw these failings as signs of a damned soul.

For Weber, the term "rational" has a broad meaning. In the context of social institutions, it implies precise calculations and increased efficiency. Things such as better bookkeeping and the growth of bureaucracy would be examples of rationalization. In the context of religion, rational implies logically consistent principles that are elaborated fully. According to Weber, Calvinism is rational for precisely these reasons. He believes that Calvinism is inwardly consistent; if one accepts its presuppositions, then it does not contain any inner contradictions. Furthermore, the doctrine of predestination reinforces the concept of God as omnipotent and all-powerful. Since God is all-powerful, then no human activity should be able to affect God's decisions. Calvinism also removed the "magic" and emotion from religion. It rejected the idea that performing certain sacraments or having certain religious experiences could lead to salvation, thus contributing to Calvinism's inner logic.