Explanations are important to users in a number of situations. They provide knowledge about how the system works, what the system knows and does, and why its actions and recommendations are appropriate. Most of the previous approaches to explanations are designed for those types of knowledge-based systems that attempt to capture the knowledge of a narrow application domain. The current tendency to move beyond closed systems to globally open ones creates opportunities but also some challenges. For example, it is a challenge for designers to cope with the dynamic and global nature of information and knowledge represented in the system as well as to structure explanations at the time of design so that they are appropriate at the time of use. This paper contributes to the current literature on explanation, by presenting a discursive framework for collaborative construction and structuring of explanations. It particularly illustrates how the model can be used for the following purposes: (a) for critical reflection on explanations at the time of design and use, (b) for management of justification-type explanation knowledge, and (c) for presentation of explanations. This paper contents that the discursive model, with its concepts and structures, provides a means for collective reflection, modification and validation of explanation knowledge. It can, thus, support the evolution of explanations along with the knowledge domain.