Boolean Logic & Proximity Operators

AND

• The Boolean AND narrows your search by retrieving only documents that contain every one of the keywords you enter. The more you enter, the narrower your search becomes.
• eating disorder AND anorexia
• eating disorder AND anorexia AND nervosa AND depression

OR

• The Boolean OR expands your search by returning documents in which either or both keywords appear. Since the OR operator is usually used for keywords that are similar or synonymouse, the more keywords you enter, the more documents you will retrieve.
• cancer OR carcinoma
• cancer OR carcinoma OR tumor OR leukemia

NOT

• The Boolean NOT or AND NOT limits your search by returning only your first keyword but not the second, even if the first word appears in the document, too.
• bulimia AND NOT anorexia

Nesting

• Nesting (using parentheses) is an effective way to combine several search statement into one search statement. Use parentheses to separate keywords when you are using more than one operator and three or more keywords.
• For best results always enclose OR statements in parentheses. AND operators should not be used inside parentheses.
• (headache OR dizziness) AND NOT (fatigue OR insomnia)

Implied Boolean Operators

• They use the plus (+) and minus (-) symbols in place of the full Boolean operators, AND and NOT.

Proximity operators (NEAR,ADJ) are only accepted by some search engines.

NEAR

• Allows you to search for terms situated within a specified distance of each other in any order.
• Using NEAR in place of the Boolean AND usually returns more relevant results.
• phylogeny NEAR ontogeny

ADJ

• Works as a pharase except that the two terms, which must appear adjacent to each other in the webpage, can appear in any order.
• Sigmund ADJ Freud (returns both Sigmund Freud and Freud, Sigmund)