Should I Include Older Sources?

 This is a question I often get from my students, perhaps because they have heard things like Your literature review has to be up-to-date or You have to know what is current on your topic.  While both of these things are true, it does not follow that you should as a matter of course exclude older sources in your field. 

While this is one to discuss with your supervisor, in general terms my view is that there is no reason to ignore older sources just because they are old, and there can be many good reasons to include them.  You can be up-to-date and deal with older sources.  As the author of the literature review, you decide what gets covered and what doesn't, and that decision should be made on the basis of what the source in your hand contributes to the synthesis you are writing, not on some arbitrary cut-off date for publication. In any field, there will be the pioneering papers, the game-changing books, the edited collections from the conference that got it all started -- the sources that nearly everyone else in your field cites.  At the very least, you should read these and know their arguments thoroughly, since they are formative in your field.  

But there is another reason why these works are valuable.  Since much of the work in your field will include an account of them, you need to know what these sources said so that you can evaluate these later accounts.  You'll find that something very interesting tends to happen with the pioneering sources.  They are cited so often in so many places that an idea about what they said enters the public consciousness of the field and a consensus view about why they matter emerges. This consensus is often based on a particular aspect of the pioneering work, or a set of aspects, or even on just on a few quotes.  Other points of equal value in the original body of ideas may simply be forgotten.  Over time, the idea of what the pioneering source said can travel some distance from what it actually said, and the consensus about why it matters is taken for granted and no longer interrogated.  These differences between what the pioneering sources actually said and what current sources say they said may be just what you need to critically evaluate the work in your field in order to suggest a new direction. 

You might also find the opposite situation -- that much of the current work in your field has not travelled very far at all from the pioneering sources and that instead of progress there are just various re-statements of problems identified several decades ago.  Here too is an entrance for new work. 

And, of course, you could find that current work has taken a good account of the pioneering works and that there is a healthy debate on a wide range of issues and you can then place your work in this on-going debate.  The only way you will know this, however, is if you have read these pioneering works and come to grips with what they said.