The modern world is based on rationalism, or the idea that we can understand our world using logic independent of direct experience. It tends to overlap with empiricism, or the idea that replicated results are the highest form of sense-experience.
From the opposite side of the debate comes the older view: human reason is misleading unless it is deeply intuitive and guided by morally honest, self-disciplined character. Our logical deductions often reflect more of the chaos of our own minds than the world around us.
In practice, rationalism means the assumption of equality a.k.a. “universality.” This thinking assumes that all objects sharing some attribute belong to the same category, and they behave the same way. It allows those objects to be treated as generic, and without any changes to our logical approach for their type versus another.
This reveals the human projection behind rationalism: we want the world to be uniform for the convenience of our thinking, which does not want to know particulars. It wants to make broad conclusions and apply them mechanically to achieve magical results. That provides the maximum convenience and ego-flattery for the individual.
Rationality starts with deduction, and ends with broad almost religious conclusions, but in the middle there is the imposition of assumptions about logic. Rationalists tend to assume that the boundaries of a category are more important than its center, in the same way the nuances of words in interpreting law has become more important than the spirit of the law. “Technically correct” is the hallmark of rationalism.
The utility of rationalism is found purely in material sciences. Technically, its results are correct, although there are always externalities and imprecisions that somehow were never noticed, and they are usually not mentioned.
If you wonder why our society is so advanced and yet so incapable of getting basic things right, you are seeing this rationalistic approach in action. When Microsoft Word glitches constantly and does by default some very stupid things, rest assured you are seeing the remnants and externalities of rationalism at work. People looked at the details and treated them as universal, instead of seeing how the parts connect up.
Rationalism has one sole advantage: it extends analytical thinking, or a bad analogue of it the way Budweiser is technically “beer,” to people who are not geniuses. The Crowd can participate if they memorize enough equations, rules and methods to be able to have some way of breaking apart a problem. But as with all things modern, the deconstructed is never assembled again into coherence, spreading entropy and misery alike.