Background: This article addressed one of the issues of research ethics that is called the nature of plagiarism coupled with involvement of intention. By definition, plagiarism is the attribution of others’ works to one’s own. This may be done intentionally and/or unintentionally. Some researchers believe that intention is not involved in the nature of plagiarism and an author who forgets to make references to the used sources has committed plagiarism since this forgetfulness has led to the attribution of others’ work to one’s own. In contrast, some experts call such a person a wrongdoer, not a plagiarist. Conclusion: By likening this problem to the issue of involvement of intention in telling a lie, the author separates two kinds of plagiarism: act-plagiarism and agent-plagiarism. The intention does not involve in the act-plagiarism (to be an act an instance of plagiarism), but it is involved in the agent-plagiarism (to call someone plagiarist). As a result, an author who forgets to make reference is not a plagiarist, but his/her act is an instance of plagiarism.
