Here’s a good way to remember what the function is of a planet, sign, and house:
1. The PLANet, makes the PLAN.
2. The Sign, carries out that plan in the style of the sign. Think of your signature, or way you like to dress.
3. The House, is where and why the action occurs. It’s the vehicle. It contains the planet and sign.
The domicile planet for Mercury is Gemini, and co-rules Virgo.
I am using Mercury Aries in the 12th house as the example.
The Planet is Mercury. It’s plan for you is to think and communicate.
The Sign is Aries. You are going to carry out this plan by thinking fast, and furiously. By being innovative, brave, and courageous in expressing your thoughts.
The House is the 12th. Poetry may be written. Poetry may be chosen as the vehicle for expression because it quiets the loudness of Aries while still making a strong impact. Aries Mercury in the 12th, requires a less direct approach since its speaker is too forward and brusque for a verbal discourse, musing, or philosophical discussion for gentler minds.
There is duplication within astrology.
Like most (if not all) languages, more than one word can be used to convey the same or more accurately — similar meaning.
Fixed stars, for example, are duplicated in other ways within the chart and vice versa. For example, my own Moon Conjunct Denebola in the 8th can be restated as my Neptune in the 10th or Mercury Semi-sextile Uranus straddling my 9th. Of course, Moon Conjunct Denebola is the most precise way of saying that what I see, many others do not.
Thankfully the language (of astrology) has been written so that you don’t need to know ALL THE WORDS (symbols, data) in order to get the meaning and understand things fully.
On FIXED STARS: Don’t want to look at the fixed stars because there’s so much doom and gloom? Ancient interpretations are not always relevant for today. Modern interpretations are necessary.
Example: Many of the fixed stars say “blindness” will occur. Do we interpret that as literal or metaphorical? If literal, we have better technology today, as well as scientific knowledge, health care, glasses, etc. so if an ‘eye issue’ crops up, modern techniques can help avoid out and out ‘blindness’. Remember when things are written. Even though some things are timeless, time changes things.
I’ve got Sag on the 11th, and 12th house and Jupiter in the 9th with Neptune in the 10th (hard to receive credit where and when it’s due until much later in life — this also shows up in a couple of my fixed stars such as Thuban and Zosma), Mars in the 7th squaring my MC, inconjunct AC, and square Saturn!