During my clinical experience I have observed that help offered to clients and client families by mental health professionals is not always as therapeutic as we would like to believe. One of reasons our assistance is not always helpful is that clinicians often assume a stance of certainty, that is, a belief that they actually know what a client is experiencing in particular context of his or her life. The problem of certainty in social work is linked to a theoretical worldview that is firmly grounded in a modernist perspective, which favors an objective view of reality based on truths that are knowable, measurable, and predictable. This worldview has dominated Western intellectual traditions for several centuries. However, despite hold that modernist thinking has on our sensibilities, postmodern worldview is bringing to our awareness other ideas that may hold significance for social work. Although these ideas have not yet been expounded to a great extent in social work literature, influence of postmodernism is being felt in clinical arena. Postmodern social work practice also looks at culture and its central place in meaning making from a new perspective. Although attention to issues of culture and meaning has always been a part of social work, holding a position of uncertainty represents a more respectful approach to cultural difference. Another important aspect of postmodern social work is an appreciation of power and many, often subtle, ways its force can be both exerted and experienced in clinical domain. Examples of forms of power that can oppress and marginalize clients include ability of workers to disseminate information throughout a system and to initiate and maintain a pathologizing discourse, as well as ways that clients make choices to concede their power to others. These forms of power frequently go unacknowledged in clinical setting, as do many other forms of institutionalized power. This article presents a call for adoption of a therapeutic position of uncertainty so that social workers may approach their work with clients in a way that is respectful of complexity of each client's life. Relativity and Quantum Theory Awareness of problem of certainty has grown during this century with increasing recognition that objectivity is an illusion. The preeminent position that notion of objectivity has enjoyed since days of Newton first came under attack early in 20th century, when Einstein's theory of relativity challenged assumptions of Newtonian physics (Prigogine & Stengers, 1984), predicated on a measurable and therefore predictable world. Relativity theory, in challenging the illusion of absolute space and time (Gleick, 1987, p. 6), dictates that a frame of reference or a context can no longer be excluded from definition of an event. Quantum mechanics theory, in opening up subatomic world, eliminated Newton's dream of a controllable measurement process. The combination of relativity theory and quantum mechanics ushered in a new era of scientific thinking (Prigogine & Stengers, 1984). Physicists soon came to realize that observer's influence on what is being observed must be included in experiment. This idea is known as Heisenberg Uncertainty Principle, and this principle formalized notion that present does not predict future (Spielberg & Anderson, 1987). The uncertainty principle states that act of observing alters behavior of what is being observed (Spielberg & Anderson, 1987); it has had a great influence on development of cybernetics of observing systems (Hoffman, 1985). In field of biology, two Chilean biologists mounted their own challenge to objectivity and brought relativistic notions into domain of life sciences (Simon, 1985). All living beings, said Maturana and Varela (1987), are structurally determined. …