In this article, the author seeks to conceptualize, with the aid of a systemic theory, the cognitive processes responsible for producing ‘defective’ translations. Accordingly, the article offers a survey of distinct types of semantic translation ‘errors’. General descriptions of their logical and cognitive features are followed by examples from selected texts. Emphasizing systemic rather than historical aspects, the author surmises: from specific ‘errors’ committed at a particular point in time conclusions may be drawn as to the poetic and translational norms prevalent at that time. Yet, the definitive correlation of a specific type of ‘error’ with a specific norm appears hardly possible. Conversely, even historical-descriptive Translation Studies have to take into account that deviations from a given source text may be caused by involuntary, invariant cognitive operations, irrespective of time.