When you are writing an academic paper, you should use scholarly sources. Here are some characteristics of scholarly literature in linguistics and literary studies:
The author should be affiliated with a university or research institute. If it is a journal article, author affiliation is often stated on the first or last page of the article. In some databases, that information is also included in the record of the source. If it is not stated in the publication or in the record, you can try to find information about the author on the web or in ORCID (a database containing information about researchers).
The text should contain a substantial number of references.
Scholarly articles are often published in peer-reviewed journals. See the following video for more information: Peer review in 3 minutes. You can limit your search to articles from peer-reviewed journals in some databases (see video). However, if you do that, other types of scholarly publications are excluded, such as academic books and dissertations. Thus, instead of limiting your search to articles from peer-reviewed journals, you can check whether a specific article is from a peer-reviewed journal. The MLA International Bibliography indicates if an article is from a peer-reviewed journal (if you click on the article's title it says "Yes" or "No" under the heading "Peer Reviewed"). If you are not using that database, you can check the journal's website to see whether they employ a peer-review process. Look under headings such as "Journal information", "Author guidelines", or "Instructions for authors". You can also use the database Ulrichsweb to determine if a journal is peer reviewed. See the video Magazine or journal? Use Ulrichsweb to find out. Note that peer-reviewed journals not only contain peer-reviewed articles but also non-peer-reviewed content, such as editorials and book reviews.
Academic books are distinguished by being published by university presses — such as Cambridge University Press, Harvard University Press and Sorbonne Université Presses — as well as other academic publishers like Routledge, Bloomsbury Academic and L'Harmattan. If it is not a university press, you can check the publisher's website to see if they state that they publish academic literature.
Student theses are usually not considered scholarly publications in the strict sense, since they are not reviewed by researchers who are experts in the field, among other things.
Although using scholarly publications can help to find high-quality literature, it is advisable to approach all sources with critical scrutiny. Authors can for example be biased and exclude information that does not support their views. Consequently, check what other authors have written on the same subject, if possible.
Unfortunately there are many articles on the web from so called predatory journals, which are low-quality and dishonest publications. Predatory journals make money by deceiving researchers into believing that they are legitimate scholarly journals and charging authors a publication fee without checking articles for quality. They also usually falsely claim that they are peer-reviewed journals and sometimes the editorial board consists of people who do not exist or who are unaware that they are listed as members of the board.
If you are using the MLA International Bibliography or the Linguistics Collection, the risk of encountering articles from predatory journals is very small, In contrast, searching in, for example, Google Scholar poses a much higher risk. Thus, if you use other search tools than the MLA International Bibliography and the Linguistics Collection, you should always check that open-access articles are not from predatory journals (check on the journal's website if it is an open-access journal). One way of doing that is to check if the journal is listed in Cabells Predatory Reports. If the journal is listed in Cabells Predatory Reports, it is advisable not to use articles from that journal. Even if Cabells Predatory Reports is continuouly updated, there may be some predatory journals that have not yet been identified and included in Cabells Predatory Reports. It can therefore be good to use other methods and resources to check that it is not a predatory journal. For example, you can check if the journal is indexed in Journal Citation Reports. If the journal is indexed in Journal Citation Reports, it should not be a predatory journal. You can also check the Norwegian Register for Scientific Journals, Series and Publishers. If a journal has been approved in the Norwegian Register (i.e. if the journal has been classified at level 1 or 2), it should not be a predatory journal. You can also check if the journal is indexed in DOAJ (Directory of Open Access Journals). If the journal is indexed in DOAJ, it should not be a predatory journal.