Dutch language in the 17th century

In the 1600's the Dutch language was beginning to modernize. The Republic shed Spain finally in 1648 with the Peace of Munster and was recognized not only as an independent country but also as a world power. Growing consciousness of Dutch as a shared language was a crucial part of that process.

Antony van Leeuwenhoek wrote in what we now call Modern Dutch, so an understanding of today's Dutch lets you read most of the writing of van Leeuwenhoek and his contemporaries. Other than the idioms, the biggest difference is the spelling. The biggest challenge, especially for those who do not know Dutch very well, is Leeuwenhoek's discursive writing style. Sentences get extended with dashes and colons and then lose their syntactical focus.

The Wikipedia has a useful overview in English of the history of the Dutch language to get you started. Also helpful is short online history of Dutch, in English, especially the 16th and 17th centuries, at the Digitale Bibliotheek voor de Nederlandse Letteren (Ditigal Library for Dutch Letters).

The best English-language discussions of Leeuwenhoek's use of Dutch:

J.I.H. Mendels' "Leeuwenhoek's Language", in Alle de Brieven / Collected Letters, vol. 4, 1952. The link will show you the English translation. The Dutch version higher on that page is much longer, but "only the parts which are of interest to the foreign reader, have been translated into English."

B.C. Damsteegt's "Syntactic phenomena in the language of Antoni van Leeuwenhoek", in Alle de Brieven / Collected Letters, vol. 9, November 1973.

B.C. Damsteegt's "Language and Leeuwenhoek", in Antoni van Leeuwenhoek, 1632 - 1723: studies on the life and work of the Delft scientist commemorating the 350th anniversary of his birthday, edited by L. C. Palm and H. A. M. Snelders in 1982.

Clifford Dobell's "Leeuwenhoek's Language", part ii (pp. 305 - 313) of the Elucidations and Annotations in Antony van Leeuwenhoek and his "Little animals". London: Constable and Company Limited, 1932. Online at Archive.org.

Burning Candle
Pieter Claesz, 1627