Zodiac Sign Gemini
© 2000, 2012 Curtis Manwaring
Gemini - May 21 - Jun 20: the twins. Keyword: "I Think". After Taurus, which emphasizes wealth, persistence and consistency, there comes a change of pace. In other words, after learning object permanence and security, there comes the learning of how to use them. This sign brings about mental application, awareness, versatility and communication and also hints that in order to see truth one must be able to see it from more than one perspective. The twins bring about this duality of perspective. One cannot know light without dark, pleasure without pain, and sameness without contrariety. It is this contrast which brings about conscious awareness, and also that which deceives and conceals, for according to Anaximander:
"The place whence things come to be, there must they pass away by necessity, for they must pay penalty and do penance according to the ordering of time." 
This sign is administered by Mercury, appropriately because Mercury is logos which functions as the go-between for the two perspectives/sects. As if to mimic the nature of this duality, Gemini is considered bicorporeal, meaning double-bodied. Note also that one cannot be more conscious of one thing without letting go of something else within the mind at any given time. Here it is Saturn, the trigon lord of Gemini by day, which provides this contrast. Here Saturn allows something to become hidden so that some critical fact comes into relief, and this is done according to the ordering of time. It is an interesting fact that without consciousness, time cannot be perceived.
Historically the meanings are very much similar to what modern astrologers are used to. We often say that Gemini's are witty, talkative, very social, sometimes superficial and duplicitous, and tend not to finish what they start, etc... Valens says:
"Those so born, then, become fond of discourse, those who work with letters and education, poetic, lovers of music, teachers of the use of the voice, capable in matters of household management, those who receive trust. They also become interpreters, those with an aptitude for commerce, critics of good and bad, prudent, curious, initiates in occult matters." 
When Gemini has the times for reputation (spirit), one becomes more flexible in their actions and often learns new skills and often they go back to school or become an apprentice. They pick up new trades or are given trusts to manage when the benefics are present or cast their rays into the place. If the malefics are present in this sign or cast their rays into it without the testimony of benefics, such will often be subject to slanders and things being said behind ones back, or accused with the spreading of rumors. Some may be pressured into a life of criminal mischief or malfeasance.
When the Twins are the 4th or 8th sign and it has the times for spirit, such may be initiated into occult matters and prone to investigate the mysteries.
More information on each of the planets in Gemini: