AND, OR and NOT are called Boolean operators.
They help connect your keywords/phrases together and narrow down your search.
In Library Search (and many databases), the AND, OR and NOT options are included within the advanced search screen. The results will group your phrases into brackets.
Alternatively, using the single search box, you can type them out.
Humans AND Evolution OR Survival of the fittest NOT Darwin
You can use brackets (parentheses) to clarify the order of precedence when you have used multiple operators. You can find out more about grouping search terms in this way.
Searching with AND ensures that all search terms are present in your results. This is useful when you are searching for something specific.
If you want to buy lunch at the deli and ask for "sandwich" you could get any filling (or worse, all of them)! To narrow your choice down, you would naturally use the AND operator when you ask for what you want.
sandwich AND cheese AND tomato
Subject searching is no different. The more specific you are, the better results you will get.
diabetes AND obesity AND female
small business AND income tax
Some search engines, like Google, automatically assume you are searching with AND. However, many library databases require you to specify how you want to search so it's good practice to use it.
There may be multiple ways of saying the keyword/phrase you want to search for. By using OR to include alternatives you may find more results.
There are some words which generally mean the same thing:
adolescent OR teenager OR young adult
Others are perhaps dialect/country based:
trousers OR pants
You may also want to combine some broader but related concepts this way, if you don't mind which of the concepts is included:
fantasy OR horror OR science fiction
If you are combining Boolean operators (see below) you will want to include a set of brackets around your OR selections to ensure they are being searched in the correct order:
farm AND (tractors OR combine harvesters OR diggers)
NOT is an operator which is used to exclude words from a search. You can force your search to ignore common results relating to your topic.
Using NOT is a bit like picking out a particular colour from a packet of sweets.
smarties NOT red
It allows you to be more specific with your subject search.
art nouveau NOT Rennie Mackintosh
primary teaching NOT maths
property law NOT intellectual
Use NOT sparingly. If you suggest a common word to exclude, you may find your results become too limited and miss some important research.
NOT can sometimes be represented with a -. In Google the search Jaguar speed -animal will exclude all references to the speed of the animal Jaguar.
You can construct a search that combines these operators.
Let's take an example from the gaming world:
adventure AND VR OR MMORPG
This search on its own will be quite confusing for the system - which should it search for first? This is where brackets are useful.
If we say (adventure AND VR) OR MMORPG we're suggesting that we want to search for VR games that contain adventure, or MMORPG games of any type.
Whereas if we say adventure AND (VR OR MMORPG) we're saying we're looking for adventure type games, which might either be VR based or MMORPGs.
To be even more specific, you may even want to combine the difference use of OR for synonyms/phrasing.
(adventure) AND ((VR OR Virtual Reality) OR MMORPG) NOT (console)