As Walter Lammi explains, Gadamer altered his predecessors’ notion of “horizon” in significant ways. Working in the tradition of phenomenology, Gadamer was of course influenced by Husserl, as well as Heidegger. Regarding the term “horizon,” Gadamer mentions explicitly his debt to Husserl. The concept of “horizon,” however, did not originate with Husserl but can be traced back to Nietzsche. We should stress up front that in each of these philosophers, the term “horizon” means something different. For example, according to Gadamer’s interpretation of Nietzsche, horizon is a “limiting concept in that human beings cannot see beyond their historical or cultural horizons” (493). For Nietzsche, it is crucial that we embrace the fact of our limited horizons; yet, in doing so, we ultimately land in despair, as we can no longer hope to find any ultimate meaning in an absolute sense. “Historicism for Nietzsche is a great but life-destroying truth because it takes away our ability to believe absolutely in anything” (494). (N.b., Lammi states in footnote 48 that Gadamer’s interpretation of Nietzsche is problematic; nonetheless, Gadamer’s dynamic concept of horizon is on target. The contents of this footnote appear in my post as note 2).
Husserl also utilizes the concept of “horizon”; however, his focus is not on horizon as a limiting concept, locking us into our diverse cultural-historical frameworks. Instead, Husserl’s understanding of horizon is much more fluid, and his focus is on the inner experience of time-consciousness, where “the horizons of one experience flow into those of another so that in the continuum of experiences there is a constant flux of horizons” (494). Gadamer comes along, takes the insights of Nietzsche and Husserl, and formulates his own notion of horizon for the purposes of his hermeneutical project. Rejecting what he understands as Nietzsche’s closed-horizon view and accepting Husserl’s less-staticized conception, Gadamer, in essence, offers a fundamental critique of Nietzsche (or what he understands as Nietzsche’s position), while de-subjectivizing Husserl. As Lammi explains,
On the one hand Gadamer, like Nietzsche, understands “horizon” to denote the finite limitations of any particular perspective at any particular time [TM, 269]. However, he interprets Nietzsche as believing that a horizon can be simply “closed,” which in Gadamer’s judgment constitutes a “romantic reflection, a kind of Robinson Crusoe dream,” [Ibid., 271] because just as no individual exists without others, no cultural or historical horizon exists in static and total isolation from others. Horizons, most particularly the horizon of the past that we call “tradition,” are always in motion just as human life is always in motion [Ibid., 217]. There is no historical consciousness in the sense of Nietzsche’s “historicist insight” that sets the horizons into motion; all historical consciousness does is make that motion aware of itself [Ibid., 271]. The awareness that our horizons are fluid, rather than teaching that nothing is true, makes it possible to find new truths-to “expand our horizons,” as the saying has it. Thus the self-awareness of historical consciousness, far from being a “deadly truth” about the relativity of all values, is for Gadamer the key for reaching beyond or behind a given horizon to confront the possibility that there is truth to be learned from the past. “I am convinced of the fact that, quite simply, we can learn from the classics,” Gadamer concludes [Ibid.,490] (494-95).
Gadamer wholeheartedly agrees with the aspect of Nietzsche’s historicist claim which emphasizes our finitude and the fact that our knowledge of our world and ourselves always remains partial and limited. Yet, Gadamer believes that Nietzsche’s historicism “fails to understand temporal distance as a positive aid to discovering which is the way Gadamer understands the interpreter’s hermeneutical situation once it is brought to self-consciousness” (495).
 Walter Lammi, “Hans-Georg Gadamer’s ‘Correction’ of Heidegger,” Journal of the History of Ideas 52:3 (1991): 487-507.
 Gadamer’s interpretation of Nietzsche is problematic on this point. Whether or not his critique is on target, however, Gadamer’s positive argument for the dynamic concept of “horizon” remains cogent.