  The opaque nature of many intelligent systems violates established usability
principles and thus presents a challenge for human-computer interaction.
Research in the field therefore highlights the need for transparency,
scrutability, intelligibility, interpretability and explainability, among
others. While all of these terms carry a vision of supporting users in
understanding intelligent systems, the underlying notions and assumptions about
users and their interaction with the system often remain unclear. We review the
literature in HCI through the lens of implied user questions to synthesise a
conceptual framework integrating user mindsets, user involvement, and knowledge
outcomes to reveal, differentiate and classify current notions in prior work.
This framework aims to resolve conceptual ambiguity in the field and enables
researchers to clarify their assumptions and become aware of those made in
prior work. We thus hope to advance and structure the dialogue in the HCI
research community on supporting users in understanding intelligent systems.
