Friedrich Waismann

From 1927 to 1928 Wittgenstein met with small groups that included Schlick, almost always Waismann, sometimes Carnap, and sometimes Feigl and his future wife Maria Kesper.

[2] Conversations from these later meetings (December 1929 up to March 1932) were recorded by Waismann, and eventually published in English translation in Ludwig Wittgenstein and the Vienna Circle (1979).

[3] This project would undergo radical transformation but the final text, inspired by WIttgenstein but very much Waismann's own work, was published posthumously in English as The Principles of Linguistic Philosophy in 1965.

He had coined the phrase “Die Porosität der Begriffe” ('the porosity of concepts') for this purpose and credits William Kneale for suggesting the English term that he then adopted.

"[10] According to Waismann, even after measures have been taken to ensure that a statement is precise, there remains an inexhaustible source of vagueness due to an indefinite number of possibilities.

[13] It is claimed, however, that Waismann's conceptualization has limited practical application, since it is more for the extraordinary, while Hart's view of open texture concerns the more mundane, approaching the term in the context of a particular norm.