| CONSTRUCTIVE THEORIES | PRINCIPLE THEORIES |
| Based on assumptions speculative in character; they gave result to a set of relatively simple formulas for explaining relatively complex phenomena | No hypothetical elements, but general properties of natural phenomena (for instance, a perpetual mobile is impossible); then all phenomena are explained through a suitable mathematical formalism |
| Most of the above assumptions concern the elements constituting the object at issue | Without constitutive hypotheses |
| Synthetic method | Analytic method |
| Completeness +adaptability, lucidity | Logical perfection, certainty§ of the fundamental principles, claim to be valid for all phenomena of the same kind |
| Statistical mechanics (Classical mechanics?) | Thermodynamics, Special relativity |