This paper is the first to perform a systematic quantitative analysis of the arguments used to motivate selections in grammatical entries from normative works on Standard Dutch written between ca. 1550 and 1650. Thus, it aims to obtain insight into what language ideologies were characteristic of this early modern period, what these reveal about how Standard Dutch took shape in its initiating phase, and what the differences are between the codification of Dutch in the early modern period (16th/17th century) and the (post)modern period (20th/21st century; analysed in earlier studies). Although certain issues within the annotation method need to be addressed in future research, the results indicate that the following principles were particularly characteristic of the early modern period: for Dutch to be a good language in terms of its grammar, it ought to differentiate, display consistency, mirror Latin and Greek, and reflect the use of certain authorities. These linguistic principles form the roots of the part of the Dutch standard language ideology (SLI; which, as previous research has shown, came into existence in the decades around 1800) that connects ‘language’ with ‘norm’ and that bestows value on the language’s regularity. However, the additional connection to social identity, that forms a second and crucial part of the SLI, played no major part in the arguments used in this time period yet. Moreover, two important differences between the early modern period and the (post)modern period were found: (1) the latter period showed a higher degree of consensus and therefore of canonisation of the normative discourse than the former period; (2) the nature of the metalanguage used in normative publications was explicitly prescriptive in the later period but mostly ostensibly descriptive/implicitly prescriptive in the earlier period. This indicates that, in terms of the metalanguage used, the normative discourse in the formative period of Standard Dutch was in between description and prescription.