The qualities are also known as the quadruplicities, which means there are four horoscope signs falls in a quality category.

If the elements tell you the person's initial impression, then the qualities will tell the person's behavior in the long run.

The following explains the three qualities in horoscope:

Cardinal: Aries, Cancer, Libra, Capricorn

Providing the ACTION to get things started.

Keywords: action, decisive, enterprising, initiating, vigorous

Fixed: Taurus, Leo, Scorpio, Aquarius

Providing the STABILITY to see things through.

Keywords: conserving, intense, persistence, reliable, resistant to change, stabilising, steadfast, supportive

Mutable: Gemini, Virgo, Sagittarius, Pisces

Providing the ADAPTABILITY to make changes.

Keywords: adaptable, changeable, flexible, variable, versatile

Qualities can explain why two person with the same element, behaved differently.

For e.g. Leo (Fixed sign) can be very stubborn on a change of request while Sagittarius can accommodate to it easily (Mutable sign).

Qualities have something gotta do with the season change.

Let's look at how the qualities of the sign progress:

Cardinal -> Fixed -> Mutable

Then, take an example on Summer, which has (Cancer -> Leo -> Virgo):

Cancer (22/6 - 22/7) represents the start of the summer. It leads the start of new season (initialisation/leading is one of cardinal sign's characteristic)

Leo (23/7 - 22/8) represents the middle of summer. It kept the summer going and is considered as the 'peak of the summer'. (therefore, the characteristic of summer is evident and therefore, translate into the 'stubborn' characteristic)

Virgo (23/8 - 22/9) represents the change of season. It sits between the end of summer and the beginning of the autumn. Therefore, the changeability of the season gives the 'mutability' characteristic.