Protoscience
In European alchemy, the three primes (Latin: tria prima) were salt (), sulfur () and mercury (). The three doshas (weaknesses) and their antidotes are the basis of Ayurvedic medicine in India. Pseudoscience
Three is the symbolic representation for Mu, Augustus Le Plongeons and James Churchwards lost continent. In Pythagorean numerology the number 3 is the digit that represents the communication. It encourages the expansion of creativity, sociability between people and movement. For Pythagoras, the number 3 was a perfect number, representing harmony, perfection, and divine proportion. Philosophy
Philosophers such as Aquinas, Kant, Hegel, C. S. Peirce, and Karl Popper have made threefold divisions, or trichotomies, which have been important in their work. Hegels dialectic of Thesis + Antithesis = Synthesis creates three-ness from two-ness. Religion
Many world religions contain triple deities or concepts of trinity, including:

The Hindu Trimurti
The Hindu Tridevi
The Three Jewels of Buddhism
The Three Pure Ones of Taoism
The Christian Holy Trinity
The Triple Goddess of Wicca

Christianity
The threefold office of Christ is a Christian doctrine which states that Christ performs the functions of prophet, priest, and king. The ministry of Jesus lasted approximately three years. During the Agony in the Garden, Christ asked three times for the cup to be taken from him. Jesus rose from the dead on the third day after his death. The devil tempted Jesus three times. Saint Peter thrice denied Jesus and thrice affirmed his faith in Jesus. The Magi – wise men who were astronomers/astrologers from Persia – gave Jesus three gifts. There are three Synoptic Gospels and three epistles of John.
Of the final three groups, the largest and most important is 
  
    
      
        
          
            
              
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  .The trisection of the angle was one of the three famous problems of antiquity.