For Habermas knowledge is internally connected to action. Habermas builds up this insight from different sources including American pragmatism and Heidegger.
About Peirce he writes:
“Peirce’s style of analysis was more up to date and hence more appropriate for a defense of the internal relations between forms of knowledge and types of action, as opposed to the limited view of logical empiricists and their focus on semantic dimension. in Jürgen Habermas, in Jürgen Habermas, Postscript to Habermas and Pragmatism, p. 227, empahsis retained
In the context of Dewey Habermas observes the following:
“Dewey directs attention to the everyday praxis in which people must “cope with” reality and “get along with it.” With this move the category of “action” (Handeln) attains an unprecedented philosophical status. Above all else, Dewey directs his attention, informed by the history of philosophy, to the seam between knowing and acting in orer to assign to philosophy a new role. Eschewing the way in which classical theory withdraws from the world, he propogates the turn toward being engaged in the world.” (Jürgen Habermas, On John Dewey's The Quest for Certainty Habermas and Pragmatism, p. 230).
Habermas mentions on several occasions the importance of Heidegger’s analysis specially in Being and Time for his work. He specifically mentions that “Our early familiarity with, and leaning towards, philosophical anthropology and the analytic of Dasein in Being and Time (Heidegger’s analysis of “being in the world” in particular had prepared us for a pragmatist epistemology.” (Postscript p. 227). It is significant here that Habermas’ mentions the concept of “being in the world” as preapring way for the reception of a pragmatist epistemology. In the similar vein Habermas asserts that “Heidegger, too, drew tacitly upon the insights of pragmatism in Being and Time, in the analyses of “equipment,” the “ready-to-hand,” and “context of involvement.” With the concept of “being-in-the-world,” Heidegger also praticipated in the anti-Pltantonic thrust of pragmatism.” (ibid.). In his lecture on Heidegger in PdoM Habermas equates the concept of Being in the world with his own conception of lifeworld:
“There belongs to situated, bodily historical existence a comprehension, however diffuse, of a world, from the horizon of which the meaning of the entities later capable of being objectified by the sciences is always already interpreted. We encounter this preontological understanding of Being when, in the transcendnetal attitude, we inquire back behind the categorical makeup of entities disclosed by transcendnetal philosophy as it follows the guiding thread of the sciences. The anlaysis of the prior world-understanding grasps those structures of the lifeworld or of “being-in-the-world” that Heidegger calls existentials.” (The Philosophical Discourse of Modernity: Twelve Lectures pp. 144)
The conception of being in the world or lifeworld is central for Habermas because it provides the basis for overcoming a limited conception of knowledge which counterpose knowledge and action on the one hand and knowledge and being on the other hand. The central epistemological lesson of Heidegger conception of being in the world and Habermas’ conception of lifeworld is this: Our ways of acting and being, our ways of knowing and acting are intertwined. The further distinction between knowledge and action, ways of being and ways of knowing would not have been possible without this prior intertwinement.
For Habermas ‘(t)he lifeworld, then, has a twofold meaning: on the one hand, the horizon-forming contexts of culture, society and personality within which communicative action takes place, and, on the other hand, the resources of possibilities from which participants in communicative action can transmit and renew cultural knowledge, establish solidarity and build social identity.’ (from here)
The lifeworld is the relam where action and knowledge, being and knowing are intertwined.
Action in the context of lifeworld refers not to instrumental action but to a holistic cocnept of action which is later developed in the form of communicative action. Here action is used as a primordial concept where knowldege is intertwined with acting in the limited sense. The influence here of Heidegger’s analysis of 'ready to hand' and his conception of 'involvement' and his pragmatic analysis of 'equipments' is all too obvious.
It is in this context that Habermas speaks of the epistemological significance of pragmatism:
“ In the Quest for Certainty, Dewey criticizes the empiricist “spectator model of knowldege, ” acording to which elementary sensations provide a firm basis for experiences. In fact, experiences are gained only in interaction with a reality against which behavioral expactions may run aground. For this reason reality is disclosed not through the receptivity of the senses, but rather in a constructive manner in the context of projecting and performing actions that succeed or fail. Objects are not “conceived” of the controlled outcome of the diliberately performed actions. Therein lies the significance of scientific experiments.” ((Jürgen Habermas, On John Dewey's The Quest for Certainty Habermas and Pragmatism, p. 231).
Habermas opposes here the spectator model of knowldege that is based on the passivity of sense experience to the one which is based on action and performance. The analysis of action and performance opens up a more complex view of knowldege which is at odd with the traditional empricist analysis of knowldege where observer is conceived as a passive receptor of data from an external world. In his more recent writings Habermas elaborates this further:
“ For pragmatists, cognition is a process of intelligent, problem solving behavior that makes learning processes possible, corrects errors, and defuses objections. Only if it served form the context of experiences connected to actions and of discursive justifications does the representational function of language suggest the misleading picture of thought representing objects or state of affairs. The mirror of nature – the one-to-one representation of reality – is the wrong model of knowledge because the two-place relation between picture and pictured and the static relation between a proposition and a state of affairs obscures the dynamics of knowledge accumulation through problem solving and justification” (TJ, p. 26).
This holistic conception of knowledge combines the Heideggerian analysis of being in the world, ready to hand, equipment etc. with what Habermas considers insights from pragmatists about what he calls innerworldly learning processes.