It’s not at all uncommon for thesis writers to use secondary sources. This term – using secondary sources – refers to the practice of reading about Text X that is relevant to your work in Text Y, and then referencing it. The reader knows that this has happened because the citation will refer to both Text X and Text Y. The citation will say something like (X date in Y date page).
Now, using a secondary source is of course absolutely fine. No examiner expects that the doctoral researcher will read everything or indeed that they will find every single original text that they reference. Some books might be out of print or just plain unavailable. Universities might not subscribe to the journals you want and not all of the missing ones will be accessible through inter-library loans.
However, if there is rather a lot of X in Y in the thesis an examiner is prone to think that the doctoral researcher has been a bit lazy. After all, in three years it ought to be possible to chase some of those key references up, particularly if they are actually widely available. For example, using a basic concept from Bourdieu or Foucault and referencing it to a secondary source – as in (Foucault date in Y date page) – looks either just slack or more worryingly like lack of knowledge of the field. Maybe their review of the literature and their appreciation of key figures and debates in the field is poor, the examiner muses. So it’s a very good idea to always try to get hold of the original if you can. And certainly, beware of using too many secondary sources.
But additional trouble comes when the doctoral researcher cites something that they think is the original source but it actually turns out not to be. This might be because the doctoral researcher has failed to take note of a citation in the text they were reading. If so, that’s careless and sloppy. Or it might be because the source that the doctoral researcher is using actually hasn’t acknowledged where they took the concept from. That’s not the doctoral researcher’s problem is it? Alas, it might turn out to be…
Examiners of course may not spot the lack of acknowledgement of a primary source. However, they are examiners because they know the field and they are thus likely to know the originals. Sometimes examiners do pick up the instances of the innocent use of a secondary source as if it’s a primary. You don’t want that if it can be avoided.
It’s always a good idea to ask your supervisor when they are reading through your draft thesis to make sure to tell you about any sources that examiners might query. Where might they be expecting to see a primary source where you have a secondary? And it’s a very good idea to check that you have picked up the original sources of ideas and concepts by always looking carefully at the citations in work that you are using and referencing.