I know this may seem a duplicate question, but I haven't find an answer to my question and I am scared to ask my supervisor. I am doing my literature review in sociolinguistics and I have different reputable sources: articles and books. Most of the authors quote the same famous works while describing that they made a contribution to the discipline. Many of these works are well known and not easy to find (old). So, is it ok if I write "[...] These themes were examinated by other scholars (e.g. Smith 1970, Doe 1977)", without having read those two books by Smith and Doe, but having read reviews and studies that explain them? I have just read a dissertation which was written in less than 1 year after fieldwork and it has hundreds or references: I can't imagine the author actually read it. It seems common to me. Can somebody clarify?
You need to be able to stand behind the claims you are making, with reasonable certainty.
To what extent reading a source before citing it is necessary for this will vary, as will how detailed any such reading needs to be. What reasonable means will also depend on the context.
If all you are claiming is that a particular source covers a particular topic, it takes very little effort to verify this. Checking the abstract would usually suffice. The risk in getting it wrong is small, so trusting other people on this doesn't seem too dangerous.
If the precise conditions of a mathematical theorem matters for whether or not it is applicable in your setting, you better double-check that the actual theorem says what you need it to say, rather than relying on an abstract, etc.
If you are weighing in on a philosophical debate, I would not trust a critic of a particular work to accurately depict the original authors views - reading the original (carefully) seems unavoidable here.
Citations typically serve three distinct purposes.
A citation can be there to substantiate your points, and to provide evidence for whatever you are saying. A mistake here can bring down an entire paper, and relying (purely) on an indirect source seems very risky here.
Citations are also the scientific currency. This means that citing a secondary source in place of a hard-to-verify original one is problematic, because it does not give proper credit. Here is where citing completely inaccessible works will show up occassionally.
Finally, (as in the example in the question) citations can be there to provide broader context. For these, a balance between taking effort to verify them, taking the literature consensus for granted, and simply not mentining them will be the way to go.
If in doubt, state that according to source X, in source Y the following happens. There is no reason here not to have Y in your bibliography. Omitting it only makes it harder for your readers to track down Y, and it can deprive the authors of Y of a deserved citation.
There are two answers that are not logically exclusive:
When you cite something, you should be reasonably certain that the source pertains to the situation and that you are representing its information accurately.
Many scholars cite materials they have not read closely, have read in parts, or that they have read through another source.
Usually, you need to read or at least consult a source in order to verify that your understanding of the source is correct.
For example, in my field (English), I read most texts I cite, since many texts are primary or archival sources that I interpret closely, or secondary sources that I engage with directly. I need a high level of understanding to respond to other scholars directly. However, there are some secondary sources that provide minor support to what I write. I skim, reading enough to understand the argument or to find the chapter or section I needed. I've never cited a source without at least looking at it.
In many STEM fields, the tendency is to cite more and with infrequent quotation. Especially in introductions or literature reviews, providing a representation of available knowledge is more important than responding to an individual author or argument. For many of these sources, the texts may have been read or skimmed, in whole or in part. For an article, they may only read the abstract and the results. How close they read those sources often depends on the level of specificity in their reference. Is it one of several works on a rat behavior, or are you indicating a specific result? At a minimum, I'd expect such authors to look at the source, even if they don't read in full.
In whatever field you're in, the presumption is that the cited fact or argument is accurate. So you are responsible for certifying that the information is accurate. If you use the source extensively, you should read it. If you use the source quickly, you should at least look at it and double-check its credibility, even if you don't read it in full. Don't rely on secondary summary alone. The Office of Research Integrity (a unit of HHS) has this advice in an article titled "Citing Sources that Were Not Read or Thoroughly Understood":
The reader should note, however, that there might be instances in which the practice of citing sources that were not read may be acceptable. For example, an author may simply wish to point out a well-known discovery or theory and provide the reader with the original citation. When this is done without misleading the reader into believing that the author read the paper detailing the discovery and is thoroughly acquainted with its contents, then no real harm is done. For example, in a paper on intelligence testing I may want to refer the reader to the psychometric properties of the X test and write: “for a review of validity of reliability of X test see reference Y”. Although I am clearly aware that reference Y reviews validity and reliability for various intelligence tests, including test X, my citation of this work does not imply that I have read and processed its contents. I am merely aware that relevant material may be found in that reference and point the reader to it. However, if in a different paper I were to write that “Smith (1879) studied the effects of X on Y and concluded that X is as important as Z and both are critical causal variables in the incidence of Y” such a statement strongly suggests that my summary of the study is, in fact, based on my reading of that paper.
ORI rightly points out that whether and how closely you need to read it relates directly to whether I'm claiming an author addresses a general topic or whether I am specifying a result. If I'm doing the latter, I had better ensure with my own eyes that I've seen and understood that result. That is why they provide this general guideline:
GUIDELINE 18: Generally, when describing others’ work, do not cite an original paper if you are only relying on a secondary summary of that paper. Doing so is a deceptive practice, reflects poor scholarly standards, and can lead to a flawed description of the work described.
The short answer to your question is no, you cannot cite works without having read them. But there is a solution:
The fact that you are reading multiple works that explain what Smith and Doe did in their research will work well enough for your literature review. If Source X and Source Y say that Smith and Doe did work on certain themes, then say "These themes were examined by Smith and Doe, as later scholars argue that they did Z" (Source X, Source Y), where Z is whatever Sources X and Y say.
While it is certainly better to read the original source material, a literature review can still be effective if you explain how you came to know what is in the original source material. Additionally, it is possible that Sources X and Y misrepresent what is in the original source material; if you cite the original with someone else's interpretation, there is a potential for many problems (both with scholarly knowledge and another with academic dishonesty).
Barring limitations like the destruction of sources, the inability to find "old" sources is usually not an acceptable excuse for not including them in a paper. There are many avenues to obtain hard to find sources, like InterLibrary Loan, for example, which should be a service you can use for free at your university. Ask a librarian if you need help.
I have just read a dissertation which was written in less than 1 year after fieldwork and it has hundreds or references: I can't imagine the author actually read it.
It is important to keep academic work honest. You would be surprised how much extra reading one does when they are passionate enough about a subject to write a dissertation on it, and besides, this is not a viable excuse for cutting corners.