Either means "one of two"; neither means "not one of two." Or goes with either, nor with neither: "Either Sarah or I will go, but neither Bill nor Jane will." When used alone, both either and neither take verbs in the singular: "Either is ready to go with you." "Neither is now ready." The use of either... or and neither... nor to coordinate more than two words, phrases, or clauses is considered permissible by some authorities but not by the majority: "Either telephone or write." "Neither Jack nor Jill knows." "He is studying mathematics, chemistry, and physics, but he is proficient in none (preferably not neither)." In either... or and neither... nor constructions, these conjunctions are properly followed by similar parts of speech or similar structures. That is, write "Either he keeps quiet or he leaves the room," not "He either keeps quiet or...."
Dictionary of problem words and expressions. Harry Shaw. 1975.