A Boolean expression is a notation that you can use to tell a search engine more about what you do and do not want included in your search. These expressions are named after the famous Irish mathematician George Boole. In Anglicans Online search, you can use the terms and and or and not, and you can use parentheses. If you have a little bit of experience with Boolean expressions you will need to pay attention to our not operator, because it is not a unary not, which is customary. Our not operator is binary, and has the meaning "but without".

The most common mistake in people's understanding of Boolean expressions is that the use of and causes you to find fewer pages, and the use of or causes you to find more pages. You might think that asking for "font and narthex" would give you the pages containing the word "font" and the pages containing the word "narthex", but in truth it gives you the pages that contain both the word "font" and the word "narthex".

Here are some Boolean expressions, what they mean, and what they do.

church and catholic	Find pages that contain both the words "church" and "catholic".
font or fount	Find pages that contain either the word "font" or the word "fount"
church and (catholic or anglican or episcopal)	Find pages that contain the word church, and that also contain either the word "catholic" or the word "anglican" or the word "episcopal".
crozier not flying	Find pages that contain the word "crozier" but do not contain the word "flying"
narthex and (font or fount)	Find pages that contain the word "narthex" and also contain either the word "font" or "fount".
(bishop or archbishop) and (diocese or archdiocese)	Find pages that contain either the word "bishop" or "archbishop", and that also contain the word "diocese" or "archdiocese"