The three classic Boolean operators that you can use to search the internet – and specifically in databases and search engines – are the simple words AND, OR and NOT.

• These (logical) operators, based on Boolean algebra, are used in a search query as ‘connectors’ to combine or exclude search terms. This results in more focused and efficient search results. Using these operators can significantly narrow down or broaden the number of results retrieved.
• Almost every search engine or database uses the Boolean operators AND, OR and NOT. In most search systems, these operators are case-sensitive, so they must be entered in upper case.

How to use the Boolean operators:

• AND: you search for both search terms, and the publications or documents retrieved contain both terms
  Example: solar panels AND urban
  Results must mention both ‘solar panels’ and ‘urban’. Both terms appear in the publications retrieved.
  This narrows down your search, as all terms linked in this way must appear in every record retrieved. Your search is more focused.
• OR: you search for both search terms, and the publications found, contain at least one of the specified search terms. Results that contain both terms will also appear in the results list.
  Example: solar panels OR photovoltaic cells
  The publications in your search results must contain either solar panels or photovoltaic cells, or both.
  This broadens your search and therefore provides more results. However, less relevant sources will also appear in your search results.
• NOT: the first search term you enter will appear in the search results; the second keyword will not appear in the results.
  Example: solar panels NOT rural
  The publications in the search results are publications that mention ‘solar panels’ but do not mention ‘rural’. Results that mention ‘rural’ – even if they also mention ‘solar panels’ – are excluded.
  Please use this search option with some caution. This method of narrowing down the search can be too restrictive and may exclude useful results. It reduces the number of results but increases their relevance.

Tip:

• If you want to exclude search terms in Google Scholar, use a hyphen (without a space after it) instead of NOT.
  Example: solar panels – rural
• In most databases, you can use AND, OR and NOT. Many of these sources also assume that two words appearing side by side implicitly imply an AND relationship.
• Some databases replace the phrases ‘all of these’, ‘any of these’ and ‘none of these’ with AND, OR and NOT respectively, usually in drop-down menus next to search fields.