Boolean logic allows you to combine search terms. Boolean operators are AND, OR, and NOT. You do not always have to write the operators yourself: Some databases have advanced searches where Boolean operators are available between search fields.
NOTE: The area in green in the diagrams signifies what is included in the search results.
NOTE: Write AND, OR and NOT operators with capital letters even if the database suggests operators with lowercase letters.
AND operator tells the database that all your search terms must be present in the search results. This reduces the number of search results. For example, when searching for materials that discuss both renewable energy and attitudes towards it, you combine the search terms with AND operator: "renewable energy" AND attitudes.
OR operator tells the database that at least one of the search words, but not necessarily all, must be present in the search results. This increases the number of search results because the database will show all the alternatives. You can use OR to search for synonyms, for example green OR renewable OR sustainable. You can also combine related terms, for example "wind power" OR "solar power", acronyms or broader and narrower terms.
NOT operator tells the database that the search term cannot be included in the search results. This reduces the number of search results significantly. Be careful when using NOT as it might exclude relevant results too. Example: "renewable energy" NOT "wind power".
See video below on how to use Boolean operators to improve your search results.
Video: Boolean operators, North Carolina State University Libraries / libncsu (CC BY-NC-SA 3.0).
You can combine different Boolean operators in your search string. When you come up with alternate search terms for all of your search topics, combine them with OR, and then combine these groups with AND. You get the widest possible search result by combining regular words (search terms/keywords) with subject terms from thesauri.
If you write the operators yourself, use parentheses to specify the order in which the search terms are searched. Terms within parentheses are read first. For example: ("green energ*" OR "renewable energ*" OR "clean energ*") AND (benefit* OR "positive effect*" OR importance OR impact* OR advantage*) AND (cost* OR price* OR expense* OR money* OR financ*). Without parentheses most databases will read the terms combined with AND first, which will change the search result.
See how to combine search terms in Finna's advanced search.
Use term truncation or wildcards to include different word endings and spellings in the search results. Truncation or wildcard is marked with an asterisk (*) or a question mark (?) depending on the database and the function you use. Truncation is useful in English search terms, because British and American English spellings vary, like in words organisation - organization, analyse - analyze, behaviour - behavior, colour - color, etc.
Check the database instructions to make sure you are using the right special character. Some databases use automatic truncation and truncation symbols are not needed.
Example from Finna:
Use search phrases if you want to search for an exact phrase (two or more words in a specific order). Search engines will search phrases marked with quotation marks in the given order and form. For example, compound words such as social media or management models would need quotation marks around them in a search.
Add quotation marks around the search phrase, for example "social media", "management models".
Many databases allow truncation inside quotation marks at the end of the last search word, for example "management model*".
You can refine or filter your search in different ways:
| Not enough search results | Too many search results |
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Use more common search terms. Search using broader concepts, for example climate protection > environmental protection. |
Use more precise search terms. Think of core concepts for your topic. Search using narrower concepts, for example waste > packaging waste. |
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Check the truncation. Do the search results include alternate spelling? |
Check the truncation. Truncating search terms incorrectly can result in extra search results. |
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Do a basic search and search all fields. |
Use advanced search and limit the search to titles, abstracts or keywords. |
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Use your own search words and phrases (together with subject terms). |
Use controlled subject terms instead of your own search words. Use the database's thesaurus to find the correct subject terms. NOTE: In some databases this may result in not finding the most recent articles in the search results. |
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Add alternative search terms, synonyms or acronyms with OR operators. |
Remove alternative search terms connected with OR operators. |
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Remove AND and NOT operators. They decrease your search results. Especially NOT can leave out relevant results. |
Use AND operators to include terms in your results and NOT operators to exclude terms you do not want in your search results. |
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Remove options that decrease your results, especially the publication type and full text filter. |
Filter your search results with different options: language, publication date, publication type. |
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Are you using the right database? |
Google, too, is a database, and like other databases it understands Boolean logic. You can improve your search results by using the retrieval techniques discussed above, such as Boolean operators and quotation marks. Please note that with Google you should use a minus sign instead of NOT to exclude a word, for example solar power -wind power.
You can use Google's advanced search to improve your results. Advanced search can be found in Settings > Advanced search.
Google's advanced search has search fields where operators are automatically added between search words, so you do not have to write the operators yourself:
Advanced search also offers many options for refining your search, such as searching in a specific site or domain, or filtering results by user rights.
NOTE: You cannot repeat a Google search and get the same results, because Google interprets your search based on your online behaviour. Even the advanced search in Google should not be used in academic information seeking.
This guide aims to support Turku UAS students and staff in information searching. It is a major part of the study materials in the Information Skills Online Course.
Finding an interesting publication can help you come up with ideas for new searches:
This resource has been licensed with a Creative Commons Attribution 4.0 International license. It does not apply to photos or videos unless otherwise stated.