Introduction

Before designing a study, it helps to examine the assumptions you are making about what exists, what counts as knowledge, and how knowledge should be produced. These assumptions—often implicit—stem from different philosophical foundations and shape decisions about how to collect data and how to analyze it.

Ontology is the branch of philosophy that examines the nature of reality. In research, your ontological stance shapes what you believe is "out there" to be studied.

Realism: An objective reality exists independently of our perceptions. A user's task-completion time is a real, measurable quantity, regardless of who observes it.
Relativism: Reality is subjective and socially constructed. A user's experience of "frustration" is not a fixed quantity—it varies with context, individual interpretation, and cultural background.

Most HCI researchers do not consciously pick a side, but their methodological choices implicitly reflect an ontological stance. Measuring error rates treats errors as objective, countable events (realism). Interviewing users about their experiences treats subjective experience as a valid and important aspect of reality (relativism).

Epistemology asks how we come to know things and what justifies our knowledge claims.

Objectivism: Knowledge is gained through detached, value-free observation; the researcher's role is to discover facts without influencing them.
Subjectivism: Knowledge is co-created between the researcher and the researched. The researcher's perspective, questions, and interpretive lens inevitably shape findings.

The relationship between ontology and epistemology is fundamentally one of logical dependence: your ontology constrains your epistemology, and together they shape your methodology. What you believe exists determines what kinds of knowledge are possible. If task-completion time is a real, observer-independent quantity (realism), then detached measurement (objectivism) makes sense as a means of accessing it. However, if "frustration" is constructed within specific contexts (relativism), no detached vantage point exists from which to observe it—knowledge can only emerge through interaction and interpretation (subjectivism). You cannot coherently embrace relativism about reality while maintaining objectivism about knowledge; there would be nothing stable for objective knowledge to reference.

Ontology	Epistemology	Methodology	Typical HCI Methods
Realist	Objectivist	Quantitative, experimental	Controlled experiments, A/B tests, surveys with statistical analysis
Relativist	Subjectivist	Qualitative, interpretive	Interviews, ethnography, thematic analysis
Pragmatist	Mixed	Whatever best addresses the question	Mixed methods, design research

Think of these levels as nested:

Ontology       →  What is the nature of reality?
  └─ Epistemology  →  How can we know about it?
       └─ Methodology  →  What methods should we use?
            └─ Methods  →  What specific tools and techniques?

Your stance at each level constrains the levels below. A realist ontology naturally leads to an objectivist epistemology and a quantitative methodology—though these mappings are tendencies, not rigid rules.

In practice, pragmatism is common in HCI. Pragmatists argue that research questions—rather than philosophical commitments—should drive method selection. This course adopts a pragmatist approach: we cover both quantitative and qualitative methods and encourage you to choose whichever best addresses your research question.

Positivism vs. Constructivism

The two dominant research paradigms in HCI can be understood as coherent bundles of ontological, epistemological, and methodological commitments: positivism and constructivism.

Positivism holds that: