The theory of communicative action emphasizes the importance of four key assumptions in the process of communication: intelligibility, truth, rectitude, and veracity. These principles form the foundation for the validity of speech acts.
These four assumptions: intelligibility, truth, rectitude and veracity, are those that form the basis of validity of speech. For Habermas, the primary use of language would be to direct its use to understanding. Language seeks to help us communicate, and in order to communicate, these four assumptions are necessary, and language “forces” us to comply with them. The other uses of language are parasitic on this ideal use.
Veracity
What he says must be what he believes or thinks; if he lies, communication breaks down.
It is for your formulation as an expression of your thought
TRUE
or also for the conditions of existence of what is said (if I say: "close the door" it is assumed that the door was open).
For the content of what is said in relation to the objective
Rectitude
If he says "you shut up" it is because he must be authorized to say it.
This would mean the following: every speaker abides by a set of rules accepted by all.
for his speech act in relation to a normative context.
Intelligibility
this is impossible if what is said is incomprehensible to others.
It is the interaction between two subjects capable of communicating linguistically and carrying out actions to establish an interpersonal relationship.