Hi Smart People of UX Stackechange community! Recently, I had this debate with some of folks in my team and I thought I should also get your valuable comment.

Assume we have following names with the associated tag: Alice (tag A and B), John (tag A), Jack(tag A and B and C)

We display the above data in a list and imagine we have a multi select drop down with the available tags to trigger a search.

multi select drop down

If the user wants to search based on tags "A and B" what should be the expected result? Should it be A and B only (Alice)? or should we also include A and B and C(Jack)?

My personal opinion is, we should include A and B and C to the result

  • What do your users say? Do they expect an 'AND' or an 'OR' search?
    – Igorek
    Commented Nov 4, 2015 at 17:32
  • Currently I dont have access to the users, but due to the nature of the data, and consistency with similar search capability in other part of the product, the expectation is AND
    – user48903
    Commented Nov 4, 2015 at 18:47

3 Answers 3


As @codeinthehole mentioned, it strictly depends on boolean logic you use in a particular filtering system.

I think that mostly useful is using conjunction (AND operator), which means that after selecting A and B from your example, displayed will be only items that has been assigned BOTH to A and B, which is Alice and Jack.

Most of the search engines work in mutual way - it would be stupid to get search results for both every website that contains keyword 'beach' and different ones which contain keyword 'boys', while user was searching for Beach Boys.

  • I did a quick search on few similar search engines, and notice the same behavior. After all, we need to make sure the behavior is consistent
    – user48903
    Commented Nov 4, 2015 at 18:52

To filter is to limit options, not expand them.

The expected behavior of a filter is to progressively narrow the list of options as tags are added. For the engineers, that means it's a boolean AND.

Providing some control that allows the user to switch this behavior on demand would be pretty cool, but that would not be the default expectation.

  • excellent point! I was thinking to allow the user to decide but our goal is to keep the feature simple with less complexity
    – user48903
    Commented Nov 4, 2015 at 18:50

It depends how the term filters utilise boolean logic.

  • AND; would include content that includes all selected terms
  • OR; would include content that includes any of the selected terms
  • I think the question is not about what would happen (given their existing booleans) but what should happen (and how they should set up their booleans) for the better UX. Given that, I agree with your answer: AND. Commented Nov 4, 2015 at 18:22
  • Fair point, but expected behaviour is going to be dependent on context. Probably best to either look at similar modes of filtering based on domain / carry out research to ensure tools allow users to carry out the journeys associated with their task. Commented Nov 5, 2015 at 12:48

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