I think that the first time I came across the pair of words 'categories and tags'1 was when I started using blogging platforms. To be frank, I am not still in a position to distinguish between them. I used both of them to 'categorize' my blog posts.
Tags2 and categories3, however are not just limited to blogging platforms. They follow me on every reading-list and bookmarking software. In some cases, they took some new names. Take for example, if I bookmark4,5 a web page on my browser, I have the possibility to add it to a folder as well as add one or more tags. Browsers, though only allow me to add a page to one folder at a time. So, there are fewer options to choose from.
So what's the confusion? I do not know when a tag name becomes a category name or vice versa. How do I decide, when to use either of these, not forgetting the possibility that I can use both of them at a time. During all these years, sometimes, I do get the impression that I understood them or at least their usage. Categories can be used to create a hierarchy, i.e, you can create sub-categories or categories within categories. You can repeat this process of creating sub-categories within categories, sub-sub-categories within sub-categories within the limits of the technical feasibility of a given software. Thus any word (or phrase) that can be part of such a hierarchy must become a category; otherwise it should become a tag. Even this definition perplexed me for a while.
Some people say that categories and tags are subjective. What's a category for one person may be a tag for another. In that case, categories and tags may have something to do with numbers. If I use a word or a phrase too many times, I should rather call it a category. And something that I will use rarely must be used as a tag. I followed this approach for a while.
Gradually, I reduced using both of them wondering if there is any particular approach to follow. Multiple articles1,6 on this topic did not come to my rescue. With the above realization that tags and categories are mostly subjective, I reached a point, where I wondered the purpose of using them. Most of the time these are redundant because they are already present in the title of the web page or bookmarked articles or in the abstract of the article. Thus, they can be easily extracted or inferred from the article content. Do we really need to add a tag with the same words that are already present in the article? Since in any case I can search for these words at a later point in time. And bookmarking, tagging and categorizing serve the purpose of possible future search queries or findability.
But sometimes, this may not be the case, we may use words that are not present in the article, but part of our thought process or a particular theme. Take for example, those one-time hashtags (tags starting with a # sign) that we use on our microblogging sites. Will these tags (or hashtags) eventually emerge as a category or a sub-category, only time will tell? Meanwhile, I continue using bookmarks (or save-it/read-it-later lists) along with the tags. And let some magical algorithms bring forth some hidden hierarchy in the future.