To what extent can we doubt certainties? How are certainties expressed in words? Which language games convey certainty? To answer these questions we have to recall the method Wittgenstein used in his investigations. When we look at language games and forms of life as inseparable phenomena, do forms of life then provide any certainty? On the other hand, do we automatically relapse into relativism once we doubt certainties? Which formal structures underlie certainty and doubt? The book is intended to answer these questions.