Systems theory differs from other theories that have contributed to the understanding of psychopathology by rejecting the notion of linear causality ("Event A caused event B") in favour of understanding causation as a set of concurrent, bi-directional, inter-related influences. Key to understanding Systemic thinking, is an understanding of how we are all influenced by feedback loops from other parts of the system (other family members, other agencies or workers), and a branch of Systems Theory is Positioning Theory, which emphasises the way individuals are drawn into taking up positions within a system for reasons that may be at least as much to do with the other parts of the system as to do with their own internal motivations and disposition. (e.g. the mother who is drawn into being the soft, forgiving parent in reaction to her partner's perceived harshness, or who is drawn into being the "housework police", ordering and bossing other family members, in relation to her partner's perceived abdication because he works as a long distance lorry driver!)

Influences in all directions

The family is then inevitably more than the sum of its members. Moreover, the psychological problems of one of its members are understood in terms of how they fit into the complex network of interactive motives and understandings that exist within that particular family, shaped as they may be by culture, by history, by biology, and by more current economic and social factors. Thus, the impact of the YP's behaviour on other family members is as critical as the traditionally (and often unfairly) promoted causative link between the parents' actions and reactions which were seen as influencing the behaviour of their child in only one direction.

Subsystems

In addition, systems are seen as containing interacting subsystems, thus parent-child or parent-parent dyads are assumed to have an impact on each other, and the inability of the family as a system to cope with and contain the YP may be understood in terms of such subsystem interactions. Within the dyads, symptoms may be understood in terms of dysfunction of the attachment system, but there is then a further level of interaction between the dyads in a complex system.

Intervening systemically

See General Systemic Techniques and FamilyWork in particular.
The aim of a systemic intervention is to identify and then deal with systemic problems that are causing the YP to be felt by the family as 'unmanageable without external intervention'. Understanding this may involve consideration of factors within individual family members, or the way that members are relating to one another, or factors outside the family (the father's work that takes him away for long periods, the mother's poor relationship with her own mother, etc.) By introducing new perspectives and information into the system, highlighting the kinds of unhelpful feedback loops that might be at work, the systemically-informed worker hopes to facilitate the system's own capacity to self-reorganise, so that new (we hope more virtuously self-reinforcing) patterns of relating can be tried out.