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It depends on your audience and/or publisher. If this is a paper for a class, you're probably fine. But if this is your thesis/dissertation or something you're going to publish, you need to see t...
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#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/41493 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/41493 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
It depends on your audience and/or publisher. If this is a paper for a class, you're probably fine. But if this is your thesis/dissertation or something you're going to publish, you need to see that earlier work. It would be one thing if you were just alluding to the concept. Listing it as one you've dismissed, for example. But you're actually using the concept in your paper. You need to have a full understanding of where it comes from. You may decide you like the original version better, or you might prefer the later one. It may also turn out that the 1969 author was being thorough but really the 1944 idea didn't do the same thing. What worries me most though is when you say "everyone else credits the 1944 source." That's a sign that it's important. There is no getting around it; you need to see the 1944 work. To be clear, I'm not saying just that you need to cite the 1944 author, but that you have to read the 1944 work.