Constructivism. This is an unpublished lecture read 5 years ago stating the program of constructive ‘Wissenschaftstheorie’ (i.e. philosophy of the sciences and humanities). Its publication now is an attempt to clarify the muddle documented in the issue 23/2 of this journal, which discussed radical constructivism (referring to biological evolution) and constructionism (referring to psychological genesis). The muddle is caused by the uncritical use of ‘elaborated’ speech (Bildungssprache) with terms such as: empirical, metaphysical, explanation, description, reality, actuality, object, entity, etc.). Constructivism as first tought in Erlangen reconstructs its own elaborated code for use in the constructive Wissenschaftstheorie. All constructions (reconstructions) start from practice with the language reduced to unelaborated talk within practice. This is called the ‘practicist’ turn of Wissenschaftstheorie. This turn is limited to scientific or humanistic disciplines supporting common action in response to precritical needs, especially war and hunger. Traditional disciplines can be reformed to serve this purpose. The lecture sketches the beginnings of such a reform for mathematics and technology (including physics as a step towards better technology) and for ethical politics – in contrast to strategies for more power – (including history as a step towards more consensus). The sketch follows the terminological proposal worked out in my ‘Lehrbuch’ of constructive Wissenschaftstheorie (1987). Logical particles are introduced dialogically, modalities are defined syntactically. The compatibility of relativistic physics with constructive theories of space and time (protophysics) is shown. For ethical politics the starting point is, that we live in states with laws enforced with respect to all citizens alike – and that we live in a post-traditional pluralism of ways of life (Lebensformen). Without the rhetoric of values and without the abstraction of human rights, it is shown how an enlightened style of argumentation can transform our states into ‘republics’ with a compatible plurality of ways of life. Whether such enlightened argumentation has a chance of being accepted by intellectuals (before they have destroyed our world) – this question remains unanswered.