Most of the texts in this collection were revised frequently by Voltaire, and numerous editions of each were issued, with or without his permission, during his lifetime. Text added to the original in the interests of clarity has been placed within square brackets. Substantial variants, as in the case of PA, have been included, as have Voltaire's own notes, with the exception of minor references. In the case of Voltaire, first editions do not often offer the most appropriate base text for modern editorial and scholarly purposes. However, important areas of text in the first edition of PA, ABC, DP and QE, subsequently suppressed by Voltaire, have been identified and restored. In the case of DP, articles having their provenance in the 1764, 1765, 1767 or 1769 editions, but which underwent further change and expansion in QE, have been listed under DP. Only articles appearing for the first time in QE have been listed under QE. In the case of both alphabetical works, the French title of articles precedes the English title so that the correct sequence can be maintained.