Which theory classification is recognized as the most concrete?

The classification recognized as the most concrete is empirical research methods. This is because empirical research is rooted in observable and measurable evidence obtained through experiments and systematic observation. It involves collecting data that can be quantified, thus allowing for specific conclusions based on real-world phenomena. This concrete approach helps to validate theories through direct experimentation and observation rather than speculation or abstract reasoning.

In contrast, abstract formulations and theoretical frameworks are often more conceptual or philosophical, focusing on the relationships between ideas rather than directly observable data. Normative theories, meanwhile, typically deal with what ought to be rather than what is, focusing on values and ethics rather than measurable facts, making them less concrete than empirical methods. Consequently, empirical research methods stand out as the most concrete classification in the context of theories.