For the past twenty years phrases such as “stable information needs”, “unstable information needs” or “information needs changing over time” are found in many contributions to information science. At first view these concepts seem to be easy and clearly understandable. However, after some considerations different questions arise: For which types of information need do we see that these needs are changing over time – for all types, or only for certain types? How do information needs relate to changes in the world, or to changes in the human understanding of the world? We will show that “information need changing over time” is a very complex concept and only understandable if we distinguish between changes in the world, situation/context, user, types of information need and interpretation of data. Clarity of writing is essential in scientific writing and authors using the concept “information needs changing over time” or similar phrases should clearly define what they mean by the phrases to ensure that no ambiguity exists when readers interpret their writings.