Protoscience and Reconstruction. A central concept of the constructivist philosophy of science is the term 'protoscience'. From an orthodox point of view, protosciences are bound to give the so called 'measurement-theoretical Apriori' for a science. Protophysics for example defines the quantities 'length', 'time', and 'mass'. Thereby it yields some basic physical laws, which usually are regarded as "laws of nature", but in fact follow already from the definitions of the basic quantities. The attempt to establish other protodisciplines than protophysics is (...) traditionally regarded as not very promising, because other sciences do not like physics build their main theories on certain basic quantities. Nevertheless such enterprises like "protochemistry", "protobiology" and "protopsychology" recently appeared on the scene. Does this mark a breakthrough in constructivist philosophy of science or is this multiplication of protosciences no more than a promotion strategy? In the article it is shown that the orthodox definition of 'protoscience' is in fact far to narrow. An alternative definition is proposed which on one hand preserves the classic tasks of protophysics but on the other hand allows for other protosciences as equally useful enterprises. A central concept within the complex topic "protoscience" is the one of 'reconstruction'. It can be shown that there is a certain ambiguity in the use of this critical concept. Therefore the article ends with a reconstruction of the term 'reconstruction'. (shrink)