Comments like 'it's natural', 'it's normal', 'it's obvious' or 'it's common sense' are everyday occurrences in the responses students make in their descriptions of physical phenomena in school science. This paper explores some of the meanings students attach to these terms and the ways in which they are used, within both orthodox science and 'children's science'. The common use of 'it's natural' leads to a discussion of experiential and explanatory gestalts of meaning, and their relationships with 'alternative conceptions' and 'alternative frameworks'. In essence it is a study of the 'taken for grantedness' that lies within both scientific explanation and students' 'alternative conceptions' in school science. The final section explores some examples taken from the contemporary research literature and from interview discussions with students conducted by the authors.