Postmodern discourse treats the current conceptual confusion as a sign of a contemporary super complex world. This conceptual confusion penetrates the "pure" shape of the university, affects its strategies of action as well as forms and curriculum. In the context of the powerlessness of traditional educational paradigms, universities try to conceptualise different techniques of knowledge construction. Problem-based learning (PBL) strives to respond to the intellectual needs of the creative society, i.e. to enable a personality to function in society together with others, despite mental chaos, ethic gaps and excess opportunities. The research on problem-based learning reveals the complexity and contextuality of the PBL phenomenon arising not only from the philosophical paradigm, conceptual problem-based learning attitudes, but also from its application context (study field, interdisciplinarity, etc.). The aim of this research is to reveal the essential PBL experience of students in constructing an interdisciplinary knowing.

Boix Mansilla (2016) states that cognitive processes involved in interdisciplinary integration have proven difficult, as "interdisciplinary synthesis can only be observed through manifest communicative efforts" (a reflection on learning). Integration is embedded in complex, often-circuitous investigative processes (Holbrook, 2013), when describing a problem to be understood, formulating questions, creating theoretical frameworks, combining methods, deploying analytical categories or when gauging the contribution of an interdisciplinary approach. (Boix Mansilla, 2016, Bergmann at al., 2012). Obviously, "interdisciplinary synthesis embodies a vast array of purposes and disciplinary combinations" (Boix Mansilla, 2016).

The investigation has been conceptually grounded in constructivism and social constructionism. Constructivist epistemological considerations appeal to the idea that individuals, due to their unique experiences, create meanings – concepts or mental representations (Berger, Luckmann, 1991, Guba, Lincoln, 1989, Crotty, 1998). Then, social constructionism regards knowing to be interactively constructed in social practices, with some practices given the advantage, and others – disadvantage (Guba, 1990, Gubrium, Holstein, 2008). Taking this perspective, a researcher seeks to identify a distinct notion of the investigated phenomenon, together with varied experiences of reality (Patton, 2015).

As PBL is multiplex and constantly changeable, any piece of qualitative research can only present a snapshot of a moment in time. The results of the present research are contextual, therefore, they can only be interpreted within the frame of a university student group which considers PBL as an innovation. Besides, this piece is a part of wider research on interdisciplinary PBL, which embraces other qualitative research methods, such as interview, observation, and others.

The present research seeks to reveal learning situations, events, and experiences, crucial for constructing an interdisciplinary knowing, using problem-based learning. The investigation aims at finding out what experiences of PBL are essential in constructing an interdisciplinary knowing. The investigation relies on ethnographic case study theory by Merriam (1998). The present research involves the purposive sample (n=16) of Social Sciences Master’s 1st year students at one Lithuanian university. Purposive sampling provides the researcher with more comprehensive data about the investigated phenomenon. The students were taking an innovative course which used the interdisciplinary PBL method. Qualitative data has been collected from anonymous written reflections (learning diaries), anonymously produced by the surveyed students who depicted their everyday PBL experience, the construction of new knowledge, and its shift along different learning stages. Reflective students’ diaries covered one cycle of PBL, devoted to the completion of a definite task. For the analysis of qualitative data, this particular research has chosen the inductive qualitative content analysis (Thomas, 2006, Schreier, 2012) which helps reveal students’ essential experiences in interdisciplinary PBL. The primary purpose of the inductive approach “is to allow research findings emerge from frequent, dominant, or significant themes, inherent in raw data, without the restraints imposed by structured methodologies” (Thomas, 2006). The application of inductive qualitative content analysis, particularly emphasizes analyzing, first, language characteristics which serve as a way of communication and, second, contents, themes, and contextual meanings (Hsieh, Shannon, 2005). Qualitative content analysis allows the classification of large texts into categories, representing similar meanings (Weber, 1990). Meanings of the text can be either directly articulated or decoded during text analysis, in total or in part (Hsieh, Shannon, 2005). Qualitative content analysis also enables the assay of interrelations among the identified major categories, noticed and recognized by the researcher, with the benefit of revealing research object’s immanent features. In analyzing qualitative data, the first impression and researcher’s intuition are important. Stake capitalizes on researchers’ impressions as the main source of data and making sense of them as the analysis (Stake, 1995). Besides, inductive qualitative content analysis requires making certain sense out of data (Merriam, 1998). which involves consolidating, reducing, and interpreting research data, making meaning, to produce a significant description of the researched phenomenon. Such a view is relevant to the constructivist epistemology. Ethnographic case study enables the analysis of all qualitative research data as a single entity.

Some authors view PBL as a tool helping students "learn with complexity, see that there are no straightforward answers to problem scenarios, but that learning and life takes place in contexts, contexts which affect the kinds of solutions that are available and possible" (Savin-Baden, 2000). In the analysis of written reflections, two main categories emerge. They characterize essential PLB experiences within the investigated group during the process of interdisciplinary knowing construction. Those are the diversity of learner identity and the flexibility of managing complexity. The question arises – what is the relationship between the two essential categories, denoting students’ PBL experiences in the process of an interdisciplinary knowing construction, identified in the present research? Students encounter the essential challenge of interdisciplinary PBL: (i) should they bracket or open their own dissimilarity, so that the group could manage its natural complexity? At the same time, (ii) how to keep the value, generated by authentic learner divergence, which enables synthesizing group thoughts or constructing a meaningful problem solving scenario, based on interdisciplinary knowing. The experiences of interdisciplinary PBL intervene between two antinomies – contradictions of the diversity of learner identity vs. a search for group unity, and the flexibility of managing complexity vs. cognitive dissonance, which arise due to diversity and complexity. Different borderline PBL experiences highlight a multidirectional students’ search for the relations between different ideas, concepts, theories, and methods so that they could avoid cognitive dissonance and would tame the complexity.

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