The fourth variation, , refers to the very special "action" of speaking or communicating with fellow human beings. Communications are such a special type of action, if indeed they are "action" in the proper sense of the term, that they require their own version of the general expression.
The implications of analyzing the act of saying a particular thing in terms of goals and side effects are troubling. If we decide what to say by projecting the costs and benefits of alternative communications S, truth and candor can easily get lost in the shuffle in the interest of expediency. Indeed, it is possible to argue that we should act in this regard according to a rule that we should not decide in this way how to speak!
Ethical considerations being placed aside, however, there is no doubt that a great deal (hopefully not all!) of human communications can be well understood in terms of the expression and its possible manipulations. This is not least so in the realm of politics. Phenomena such as demagoguery, sycophancy, campaign oratory, and propaganda clearly lend themselves to analysis in these terms, so does censorship, jamming, and other methods of preventing communications.
The special importance of the act of communicating in human life is implicit in the history of the struggle for freedom of speech. Organizationally, this has been embodied in the free speech clause of the First Amendment. Probably the single most important change in the Soviet Union in this light was the rise of glasnost after 1985.