Can articles be assigned to multiple categories or sections?
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This article is for Joomla! CMS Version(s) 
No, Articles and other content items cannot be assigned to multiple categories or sections.
In Joomla! and : Content items are restricted to a single category in a single section. In Joomla! and newer: Content items are restricted to a single category in a category tree.
Possible work-arounds include:
- creating duplicate articles in multiple categories.
- using menus rather than dynamic lists of content items.
- using various third party extensions that simulate assignment to multiple categories.
- using key words to simulate categories and sections.