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According to logical positivism, a scientific theory is an axiomatic system
that obtains an empirical interpretation through appropriate statements called
rules of correspondence, which establish a correlation between real objects
(or real processes) and the abstract concepts of the theory.
The language of a theory includes three kinds of terms:
 Logical terms, which include all mathematical terms.
 Observational terms, which denote objects or properties that can be directly
observed or measured.
 Theoretical terms, which denote objects or properties we cannot observe or measure
but we can only infer from direct observations.
According to this distinction, the statements of a theory are divided in three sets:
 Logical statements, which include only logical terms.
 Observational statements, which include observational and logical terms.
 Theoretical statements, which include theoretical, observational and logical terms.
Theoretical statements are divided in:
 Pure theoretical statements, which do not include observational terms.
 Mixed theoretical statements, which include observational terms.
The following table represents the diverse kinds of statements.
Statements

Lstatements

Ostatements

Tstatements

Pure Tstatements

Mixed Tstatements

Lterms

Lterms

Oterms

Lterms

Tterms

Lterms

Oterms

Tterms

(Abbreviations: L=Logical, O=Observational, T=Theoretical)
