Boolean Logic allows you to combine keywords to make a search more precise. The three terms are: AND, OR, NOT.
AND - Narrows a search
Example: medial collateral ligament AND therapy: Retrieves articles with both medial collateral ligament and therapy.
OR - Expands a search
Example: medial collateral ligament OR mcl: Retrieves articles with just medial collateral ligament, just mcl, and articles with both medial collateral ligament and mcl.
NOT - Removes a term from a search
Example: medial collateral ligament NOT mcl: Retrieves articles with medial collateral ligament, but remove all articles with any mention of mcl. Use NOT sparingly because you often lose many useful articles.
Boole was born on Nov. 2, 1815, in Lincoln. He attended a primary school of the National Society and then a school for commercial subjects. This was 
the last of his formal schooling but not the end of his education, for he inherited a talent for self-study from his father, a shoemaker by trade but a philosopher by inclination. At the age of 16 young Boole became an assistant teacher in an elementary school. Four years later he opened his own school. In 1844 Boole's pioneering paper on the calculus of operators won the Royal Society's gold medal and established his reputation among mathematicians. Three years later he published The Mathematical Analysis of Logic, the slim booklet that initiated modern symbolic logic.
Boole married Mary Everest in 1855; she bore him five daughters. Their life together was serene but short, for Boole died on Dec. 8, 1864, of pneumonia. The citizens of Lincoln installed a stained-glass window in the Cathedral to his memory.
Boole's reputation continues to grow. In 1847 he pointed out that the value of his theories would depend largely upon the extent of their applications. Today, along with symbolic logic, Boolean algebra is of central importance in such diverse fields as probability, combinatorial theory, information theory, graph theory, switching theory, and computer design.