There is still uncertainty about the relationship between the two terms that shape German tenancy law: "Mangel" and "vertragsgemäßer Gebrauch". The dissertation critically assesses the views expressed on this subject in the case law and academic literature, traces the historical development of the warranty law and the subjective concept of defect, and concludes that a defect of the leased object understood as a deviation from the agreed quality coincides with the impairment of its usability.
