There is much less continuity and firmness than with the Sun, but more plasticity, variety, change and adaptability. The mind responds more readily to new ideas; mental habits are less firmly fixed and ingrained; there is a tendency to change opinions, perhaps several times during the life, or even to entertain apparently contradictory ones.
This may be taken as a tendency on the part of the mind to combine with the emotions, to be influenced and modified by them, and to harmonise and co-ordinate them in its turn. It lends itself to a variety of uses of all degrees of superficiality or profundity, according to circumstances.
This is seen when the planet is in Leo or is in close conjunction (say 5°) with the Sun. Strength and vitality are given to the mind as a whole rather than to any subdivision of it. Prompt response to new ideas does not occur so readily as with some of the combinations;
Here the fire and passion of Mars are blended with the intellect. In undeveloped natures, this means that the reason is constantly in danger of being swept aside by storms of passion, desire, anger, prejudice, or self-will. In higher natures, the mind overcomes such impulses and utilises them as energies to subserve its own ends.
This may tend in one or two directions. Firstly, the mind may go out towards mankind showing interest in all studies, pursuits, or occupations that relate the native to his fellow men. It shows in various ways, from cordiality, sociability, good nature—the prudent adviser, the helpful friend —up to the wider operations of philanthropy and benevolence in the world at large.
The effects of this combination may vary a good deal according to the type of horoscope, the aspect, and the relative strength of the two influences. At its best it gives a very comprehensive and profound mind, capable of achieving much in whatever direction it is turned. The memory is good and strong, and the judgment sound and sensible.
In any aspect the mental power is much increased, and may gain either in activity or profundity according to the type of horoscope. There is originality, ingenuity, and inventive ability. Generally some distinct ability for such subjects or pursuits as are indicated by Uranus is shown, and they may be taken up with interest and successfully carried out, unless the aspects are very adverse.
The mind gains in receptivity, plasticity, adaptability, and intuition. Any tendencies in the direction of the higher mental emotions and powers of imagination will be increased and may work out in various directions, art, poetry, music, etc., according to the general type of horoscope.
When in its own sign, Gemini or Virgo, Mercury might theoretically be supposed to exhibit mind per se, uninfluenced by any special mode. In practice, however, this never happens; because the heavenly body with which it is in closest aspect has then to be taken as significant of the type.
Mercury in the third house indicates one fond of learning, studious and generally mirthful, alert, and active mentally. Eager to investigate science, or any new thought, fond of reading, literature and all things that enlighten and tend to expand the understanding. This house is wholly mental, being (analogically) the positive station of Mercury : it therefore gives a love of writing and speaking, and tends to quicken all expressions of the mind in every form.