Here's my situation: I'm writing a paper for a history class on the topic of changes in the US economy between 1896 and 1936. More specifically, I'm looking at the positions of different American industries in relation to their international competitors and how they changed over this period, and how those changes affected the party system that emerged in 1896. There's good secondary sources on the trajectory of major industries that I've found, but it seems a lot more difficult and complicated to try to cobble together what the secondary sources say by using the primary sources.
I'm an undergrad, and my prof wants all the papers to rely on primary sources. I can't help but feel that in my paper's case this rule doesn't really make sense, as it's just a very big project if I try to prove my points using primary sources and a pretty simple one if I use secondary sources. But maybe I'm being lazy, and good history is always done with primary sources. Do you guys have any thoughts on this?
First of all, this sounds like a topic that is incredibly broad. Broad enough to do a Master's thesis on, rather than just an undergrad paper. I would strongly suggest narrowing it down to focus on one industry or one aspect of your topic that you find most interesting. Sometimes, it's easiest to do the research and then isolate your topic, based on what you've found. Often, research can turn up new ideas or fail to support what you wanted to write about, so you end up going in an entirely new direction.
Primary sources, when available, are pretty important and this is a resource that your professor really wants you to make the most use of. When you use secondary sources, you're basically just using someone else's research. It's fine to get ideas from what they've analyzed, but equally important to counter their ideas or evolve them further. I usually use the footnotes and bibliographies of secondary sources to find out what primary sources they used. I then read over those sources to see what additional information I can find to support my own research leads and include them as primary sources. I know it's a lot of work, but digging around can be really fun. You can also delve into unique primary sources such as interviews, news stories, and advertising to flesh out a subject like this one.
Go and consult your tutor for advice. My £0.01 is that you shouldn't be 'trying to cobble together what the secondary sources say using primary sources', instead try and source stuff like contemporary diary entries or other more neglected 'primaries' and make your own argument. The idea of a good (and highly-marked) history paper is to formulate your own ideas instead of just echoing prior consensus.
/u/prettyslattern's answer is essentially on point (especially on the breadth of your question).
All I would add is that you will still need to cobble together your secondary material to provide a historiographical overview. When you read your 'trajectory' material think about what individual historians have omitted or got wrong and why. Is the problem in their methodology or their focus? This is the spine around which your introduction is based and rests on knowledge of the primary material. Your essay might want to say something meaningful or useful but then you need to explore why no-one else has bothered to say it before. Have they been overlooking a certain source or misrepresenting another?
Secondary material is a jumping off point. Usually if you can't find that point within your secondary reading then you're covering a topic which has been done to death (in which case you must read the primary sources to find a new angle). I don't think this is the case here, although it sounds more that you've found yourself at the top of a cliff and can't see over the edge. Find a smaller, narrower, and less steep precipice.
A handy trick is to just go around and look at the different primary sources used by your secondary sources. It's not plagiarism or cheating because you could interpret the data in a far different manner.