Using Parentheses (or Curved Brackets)

Parentheses or Curved Brackets should be used to group search terms when combining three or more terms with different Boolean operators, to indicate the order of search. Terms enclosed within parentheses/brackets are processed together first by the search engine.

For example, the following query searches for documents containing care and also containing either cat or dog:

care AND (cat OR dog)

Without parentheses/brackets, the query <care AND cat OR dog> searches for documents containing care and cat, or containing dog, so would bring back many results about dogs unrelated to care.

Multiple sets of parentheses/brackets should be used in longer searches that combine multiple phrases together with Boolean operators, to designate clearly to the search engine how the search should be processed.

Searches within parentheses/brackets are performed first and parsing proceeds from left to right. Parentheses/brackets must be “balanced” around phrases so that both longer compound phrases and their shorter sub-components within are correctly enclosed in parentheses/brackets on either side.

In the search example below both variants give correct results because the phrase on the left contains balanced parentheses/brackets.

((pet OR animal) AND (interaction)) AND ((blood pressure) OR (cortisol reduction))

gives 2287 results

((pet OR animal) AND interaction) AND ((Blood pressure) OR (Cortisol reduction))

also gives 2287 results

By comparison this third variant contains unbalanced parentheses/brackets on the left (a second extra right parenthesis/bracket) and gives 0 results:

((pet OR animal) AND interaction)) AND ((Blood pressure) OR (Cortisol reduction))

The search results query text rendered immediately above Search Results shows you how the search has been parsed.

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