The Third House represents your lower mind, repetitive thoughts, words, deeds (behaviors), siblings and neighbors. In this house your communications with your siblings, relatives, neighbors and friends are reflected.
This is your house of inner emotions and it reflects your mental aptitude and attitude, reflecting anything requiring communication. The twins become your conscious mind and your unconscious mind.
Dividing your responsible side from the irresponsible, you show to the world which twin truly rules in this house. Knowing which twin is in control, can tell you much a lot about yourself.
In the physical body, the Third House rules the vocal chords, speech, fingers, arms, hands, shoulders, lungs and nervous system.
The octave to the Third House is the Ninth House. Whereas the Third House rules your lower mind, the Ninth House rules your higher mind and bigger picture of life. This is where you ascend from content details of the lower mind to larger concepts of your Soul mind.