The mutable quality is last of the three. Cardinal intiates, fixed keeps it going and mutability fills in the gaps. The mutable quality accommodates, mediates; it adapts. The four mutable signs are Gemini, Virgo, Sagittarius and Pisces. Mutable houses are the 3rd, 6th, 9th and 12th. Mutables find a way around obstacles and fill in the spaces.
Gemini is the air element mutable, Virgo the earth, Sadge the fire and Pisces the water. To use water as an example, think of a huge boulder in the river bed. A boat might have trouble getting around it but not the water. The water flows, over, around. Mutables have less trouble changing course than do other qualities. They flow: air, earth, fire, water, in mutable they find a way around, naturally.
Cardinal and fixed modalities have their own ways of addressing obstacles, this is different. Cardinals initiate a new course of action. Fixies hammer at it. Mutables just go around. Changing course is expected because change is expected. Accommodation is accepted.
The mutable houses show the areas of life and function where we fill in the spaces left behind by the initiators and the workers before we move on to the next phase of construction. Gemini is there with its canned air, Virgo with its fill dirt (or duct tape), Sadge with its blow torch and Pisces with its garden hose (or fifth of tequila).
Do you have planets or placements in mutable signs or houses? Do you go with the flow, let things go, in these areas?