This paper is an attempt to establish an objective criterion for civilizations, in order to treat them impartially and give them a fair assessment. First, theories up to the present about civilizations including those of Spengler and Toynbee are introduced. Second, the criterion presented by Bagby to distinguish major civilizations and peripheral civilizations are examined and proved to be subjective. Then the author proposes as an objective criterion for big civilizations just the pattern of succeeding four stages with the span of 400~500 years each. Big civilizations meeting this requirement which total eight or nine are divided into two types according to the difference of their nature. Lastly is shown how four puzzles of world history that have hitherto caused a lot of disputes (feudalism, absolute power of royalty, capitalism and modernization) can be solved through the recognition of these big civilizations.