A core impetus of participatory and action research is making science relevant and useful for solving pressing problems and improving social conditions, and enabling stakeholders to participate in research and development processes. There are claims in the community of participatory and action research of the potential for heightened scientific excellence, but at the same time, there are critiques in the mainstream community that more engaged, even activist, stances threaten scientific norms or that position these type of research approaches outside the field of science, for example, as issues of application. In the search of clarification of the scientific identity and the specific qualities of participatory and action research, scholars have been moving away from and sometimes have rejected traditional conceptions of quality. This leads to confusion about how to relate to the discourse on research quality and scientific excellence in mainstream science. Integration in this discourse is important in order to attain academic legitimation in prevailing institutions of science, for example, in applications for funding, in seeking to publish research, and in the acceptance of dissertations based on participatory and action research. The purpose of this article is to contribute to this integration by reconstructing the way traditional quality concepts - validity, reliability, and objectivity - can be fruitfully used in expanded frameworks for quality where scientific excellence of participatory and action approaches are visible and where mainstream science approaches also can be harboured. In this conceptual article, reconstruction of understanding of scientific inquiry is first made based on a praxis-oriented epistemology inspired by pragmatism. Through rethinking truth as trustworthiness, new proposals for the conceptualization and frames for research quality and scientific excellence are introduced. Second, a framework for understanding purpose in science and its basis in validity, reliability, and the core characteristics of participatory and action research is developed. Third, the turn to action, practice, and participation enables plural ways of knowing and ways that knowledge claims can be validated and made trustworthy. The article concludes that participatory and action research offers a broader landscape of purpose and validation than more traditional approaches to science. In a subsequent article, reliability and objectivity, and their use in participatory and action research, will be clarified.