Philosophy of Being and Knowledge

Philosophy of Language

Gottlob Frege

At the heart of the philosophy of the German logician Gottlob Frege (1848-1925) is the distinction between two categories: sense (German Sinn, English Sense) and reference (German Bedeutung, English Reference). When any linguistic form (such as a proper name, concept, or sentence) is used, the speaker simultaneously refers to two realities: the object itself and the body of knowledge about that object. The object itself and the object as reflected in knowledge are not the same. Frege used the term "reference" to denote the actual object being talked about. Accordingly, the object is the reference of the utterance, since any utterance points to the thing it discusses. For example, the reference of the word "Sun" is the star at the center of our solar system. The term "sense" for Frege referred to all the knowledge that a speaker’s environment possesses about the object being mentioned. For instance, the sense of the word "Sun" encompasses everything humanity knows about the star at the center of our solar system. The sense and reference of an utterance do not always coincide. Frege’s favorite example to illustrate the difference between sense and reference is the terms "evening star" and "morning star." Both terms have the same reference, as both refer to the planet Venus. However, their senses differ, as it was not always known to humanity that the evening star and the morning star are the same planet.

Frege emphasized that sense is not subjective knowledge of an individual. The sense that a speaker imparts to an utterance is the same as the sense that a listener derives from hearing the utterance. Otherwise, communication would be impossible. Sense expresses knowledge about the object and cannot be reduced to subjective impressions of an individual.

To demonstrate the objectivity of sense, Frege introduced another category—concept—meaning the subjective associations of each individual. Thus, the reference of an utterance is the object itself, the sense is the general knowledge about it, and the concept is the personal associations evoked by the utterance. For example, the reference of the term "evening star" is the planet Venus, the sense is everything humanity knows about Venus, and the concept includes the romantic associations that a listener might have.

Frege distinguished three types of utterances: proper names, sentences, and conceptual utterances. In each of these, the distinction between sense and reference operates differently:

• Proper Names: These are utterances that denote a single object. For example, "evening star" and "morning star" are proper names. The sense of these utterances is the knowledge about them, while the reference is the planet Venus.
• Sentences: Determining the reference and sense of sentences is more complex because they consist of several words. Frege argued that the sense of a sentence is the thought expressed by the speaker. Every speaker utters sentences to express their thoughts and convey something to the listener or reader. Thus, the sense of the sentence "Socrates is a great philosopher" is the thought that Socrates was a great philosopher. This thought, which the speaker conveys through the sentence and which is its sense, is not subjective any more than the sense of a proper name. The thought expressed by the speaker is understandable to the listener and reflects an aspect of reality, thus being objective. Therefore, the sense of a sentence is the thought expressed by it, that is, the information conveyed by the speaker and received by the listener or reader. The reference of a sentence is its truth value—whether it is true or false. Every sentence is characterized by its truth value, which Frege referred to as the reference of the sentence. When substituting senses ("evening star," "morning star"), the reference (Venus) remains unchanged, just as substituting senses in sentences does not alter their reference. For example, "The first President of Ukraine was elected head of state in 1991" and "Leonid Kravchuk was elected head of state in 1991" express different senses but have the same reference. This reasoning is known as Frege's Principle (Frege-Prinzip). According to this principle, two sentences with different senses have the same reference if the reference remains unchanged when terms and senses are replaced. Thus, the sentences "I am looking at the evening star" and "I am looking at the morning star" are identical in reference because both refer to the same object—Venus.
• Conceptual Utterances: Frege referred to judgments containing a proper name and a concept that represents a class including the object denoted by the proper name. For instance, in the sentence "Berlin is the capital," the proper name "Berlin" and the concept "being a capital" are present. The sense of such an utterance is the general concept ("being a capital"), which is the information the speaker attempts to convey. The reference of a conceptual utterance is its truth value, or its permissible use. Frege formalized conceptual utterances using the logical function "F(x)." In the given example, the concept "being a capital" is the function (F), and "Berlin" is the variable (x). If "Paris" is substituted for the variable, the function's reference does not change, as Paris is also a capital. However, if "Lviv" is substituted, the reference changes, as "Lviv is a capital" is false.