8.3 Physical necessity

The sense of logical modalities is easier to understand, comparing them with physical, or ontological (existential) modalities.

Physical modalities are concepts used to formulate statements about what is necessary, possible, random, and impossible not in thought, but in nature.

For example: “It is necessary that the action is equal to counteraction”, “It is accidental that the glass was broken”, “It is impossible for it to rain for forty days and nights in a row”, etc. Logical modal concepts are connected with the “mechanics” of human thinking and are used to characterize its essential points. Physical modal concepts relate to the device of the real world itself.

Physical necessity is a characteristic of a statement, the negation of which is incompatible with the laws of nature.

Physically necessary are, for example, statements: "All the planets revolve around their own axis" and "An electron moving in a stationary orbit does not radiate energy." Denials of these statements would contradict the laws of physics: the negation of the first statement is incompatible with the laws of celestial mechanics, the negation of the second - with the laws of quantum mechanics.

Physical ability is a characteristic of a statement that does not contradict the laws of nature.

For example, the statement “The efficiency of an internal combustion engine is 100%” contradicts the laws of thermodynamics and, therefore, is physically impossible. The statement “The efficiency of such an engine exceeds 20%” does not contradict the limitations imposed by thermodynamics and is physically possible.

Physically by chance, for example, that this car is painted green: there are no laws of nature that would prescribe it to be green or, say, blue.

Logical necessity is stronger than physical: everything that is logically necessary is also physically necessary, but not vice versa. In other words: the laws of logic are also laws of nature, but not vice versa. If, for example, the planet rotates, then it rotates - this is a consequence of the law of logic and, at the same time, the necessary truth of physics. But the fact that the planets have elliptical orbits is a law of physics, but not logic: it is logically possible that the orbits of the planets are circular.

Physical necessity is not reduced to logical. We cannot, for example, reduce the principles of mechanics to the laws of logic.

The logical possibility is wider than the physical possibility: the possible is physically possible and logical, but not vice versa. For example, absolutely pure gold that does not contain impurities is possible logically, but it is physically impossible. The circular orbits of the planets are possible logically, but physically impossible.

The widest category is thus a logical possibility. It includes physical capability and, further, physical necessity and logical necessity. The latter is the narrowest category.