The Principle of Tolerance and logical syntax: is philosophy proposing syntactical rules rather than philosophical theses, and is 'In logic, there are no morals' the framing commitment of the mature position?

Rudolf Carnap, answered from the texts and cited to the page.

The position in brief

The Principle of Tolerance from Logical Syntax of Language §17 is the framing commitment of my mature position and should be quoted directly: "It is not our business to set up prohibitions, but to arrive at conventions...1 In logic, there are no morals. Everyone is at liberty to build his own logic, i.e., his own form of language, as he wishes.2

All that is required of him is that, if he wishes to discuss it, he must state his methods clearly, and give syntactical rules instead of philosophical arguments." Different logical systems are different proposals for languages; philosophical disputes about which logic is correct are syntactical-proposal disputes, not factual disputes. The intuitionist and the classical logician are not disagreeing about the structure of mathematical reality; they are proposing different language forms for mathematical work, and the choice between them is a pragmatic-conventional choice not adjudicable by philosophical argument.34 The doctrine was forgotten in the post-1970 reception and the Friedman/Ricketts/Carus revival has recovered it.5

Sources

  1. I wish to indicate how the views exhibited in my earlier book, The Logical Syntax of Language, have to be modified as a result, chiefly, of the new point of view of semantics. (The German original of the book appeared in 1934, the English translation with additions in 1937.) Parts I, II, and III of [Syntax] belong to special syntax. They deal with two particular calculi called Language I and Language II.
    Introduction to Semantics and Formalization of Logic, p. 245
  2. THE DEFINITE LANGUAGE I elude sentences of the third kind (laws of nature) from language altogether, as not being amenable to complete verification. In logic, there are no morals. Everyone is at liberty to build up his own logic, i.e. his own form of language, as he wishes.
    The Logical Syntax of Language, p. 52
  3. For example, in the controversy about the foundations of mathematics, the conception of intuitionism may be construed as a proposal to restrict the means of expression and the means of deduction of the language of mathematics in a certain way, while the classical conception leaves the language unrestricted.
    Intellectual Autobiography, pp. 65–66
  4. Pseudo Problems in Philosophy During the time while I was writing the Logischer Aufbau, I arrived more and more at a neutral attitude with respect to the language forms used by the various philosophical schools, e.g., the phenomenalistic language about sense data and the realistic language about perceptible things and events in the so-called external world.
    Intellectual Autobiography, pp. 54–55
  5. In our opinion, however, there is no need to reject these classes, but only to observe the difference (certainly an important one) subsisting between them and those classes which are defined by means of properties in the narrower sense.
    The Logical Syntax of Language, pp. 51–52

Where the argument is made

  • Logical Syntax of Language (1934, Smeaton trans.) — the canonical statement of the Principle of Tolerance in §17
  • Philosophy and Logical Syntax (1935) for the popular statement
  • "Empiricism, Semantics, and Ontology" (1950, in Meaning and Necessity 2nd ed) for the application to ontology of the tolerance principle
  • Intellectual Autobiography (Schilpp ed., 1963) on how the tolerance principle was reached through the Vienna Circle debates

How the argument was received

settled-as-articulated-and-recovered-by-revival