Critical editions contain texts that have undergone a rigorous and scholarly editing process. This typically involves establishing an authoritative text or translation based on close readings and bibliographical analyses of a variety of original manuscripts and/or printed sources. Typically such editions also include detailed introductions to the subject and the text, annotations and explanatory notes, and an explanation of the editorial practices followed. For these reasons it is always best to work with a critical edition when one is available (often they are not).
If you are undertaking work on a particularly obscure figure you may find that, not only have his or her works never recieved the honour of a critical edition, they may also have remained out of print for centuries. Use the following resources to uncover early printed editions of works published in English between 1475 and 1800.
You can also search the Library's catalogue for printed and online critical editions not included in InteLex Past Masters. You can begin by searching for a philosopher by last name and including the phrase critical edition in your search. You may also need to conduct a more laborious review of our collections by examining the physical copies held by the library to determine if they are in fact critical editions (this will be made clear in the introduction to the volume). In many cases you will doubtless discover that a critical edition of the work you wish to study has never been published.