There are two main theories applied to relationships, Social Exchange Theory and Equity Theory underpin commonly used behavioural therapies such as Cognitive Behavioural Therapy, Enhanced Cognitive Behavioural Therapy and Integrative Cognitive Behavioural Therapy. More recent studies in neuroscience and behaviour and the importance of language have led to the development of Relational Frame Theory and Acceptance and Commitment Therapy as an alternative approach. In this essay I will outline the relationship models comparing and contrasting them. I will also introduce and briefly touch on Relational Frame Theory and Acceptance and Commitment Therapy as an additional approach to couples counselling and offer considerations which an
Elaine Hatfield worked closely with Walster and Ellen Berscheid in the seventies to understand the human concept of social justice. She says

According to Equity theory, people feel most comfortable when they are getting exactly what they deserve from their relationships—no more and certainly no less. Handbook of Theories of Social Psychology.
Hatfield, E. & Rapson, R. L. Glyph International 2011.

She also says of her work with Walster and Bercheid

We believed that a concern with fairness was a cultural universal. We were convinced that during humankind’s long evolutionary heritage, a concern with social justice came to be writ in the mind’s “architecture” because such values possessed survival value. Such concerns were maintained, we thought, because behaving fairly continued to be a wise and profitable strategy in today’s world. Handbook of Theories of Social Psychology.
Hatfield, E. & Rapson, R. L. Glyph International 2011.

It is recognised that throughout history, societies have had different visions as to what constitutes “social justice,” “fairness,” and “equity” and that these differences still influence perspectives on what social justice means to the individual and to different societies across the globe. Furthermore their ongoing research takes into consideration the current shifts within society towards gender equality and how this influences relationships. Equity