The hermeneutic spiral encapsulates the act of understanding or interpretation. Understanding, according to
hermeneutics, is always historically located, within a tradition credited with authority, from the viewpoint of whoever wishes to understand. So we never understand something as given, but always as something, having a pre-understanding or anticipation of what it is we engage with or are looking upon, just as when we read a particular part of a text, we always already have some grasp of that text as a totality or a whole. This prejudice (prejudgement) is considered essential to understanding, it is not a barrier but the medium of understanding. If modified in an interpretive encounter with something we desire to understand it forms a new basis of the next engagement, and so on: this is the hermeneutic spiral.
Implicated in the hermeneutic spiral is the problem of the seeming universality of hermeneutics - that is, if all understanding is also a pre-understanding, then there is no point from which to make external judgements, independent of tradition, and this has serious consequences for a critical hermeneutics which wishes to provide a critique of the power structures implicated in a tradition.
References
Hodder, I., 1999:
The archaeological process. An introduction, Oxford.
Thomas, J., 2004a: The great dark book. Archaeology, experience, and interpretation, in J. Bintliff (ed.) A companion to archaeology, Oxford, 21-36.