The larger theoretical question addressed in this study is whether we find a parallel development from certainty to uncertainty in several languages. My contribution to this question is a case study of surely, certainly and no doubt on the basis of the English-Swedish Parallel Corpus and the Oslo Multilingual Corpus. It is shown that in English, Swedish, German, Norwegian (and French), expressions of certainty can also perform the opposite function of ’uncertainty’. The regularity of this development is explained in terms of grammaticalization. It is argued that it may be useful to distinguish a subsystem of modal particles/discourse particles in English including certainly, surely which is derived by grammaticalization. The seeds of this development may be modally harmonious combinations of modal auxiliaries and adverbs. The translations in the corpus are used as a tool to disambiguate the meanings of strong and weak certainty in the source language items.