The 4th house corresponds to a water sign and is therefore a house of moksha (self realization or final liberation).
Mother, the heart (emotions and passions), happiness, land, fixed assets, buildings, real estate, ancestral inheritances, comforts, conveyances (cars, boats, planes), academic degree, endings, close of life, private affairs, farms, graves.
The 4th house most notably signifies the home, mother, and conveyances. It also, however, governs happiness and the heart. Therefore it is to be considered that any planet occupying the 4th reveals the passions ingrained in one's heart. Capricorn ruling the 4th would signify a passion for business, whereas Libra, a sign of Venus, would give a love of art. Although the attraction may not dominate one's career choice, it is part of the person's heritage and will remain so for life. The 4th also governs the educational degree, and therefore even if the education house (the 2nd) is weak, one may still obtain a degree if the 4th is well fortified.
The karakas, or indicators, of the 4th house are Moon and Mercury.
The retrograde 4th lord — karmic relationships and debts towards the mother. Makes it difficult to express emotions.
Source: «Ancient Hindu Astrology for the Modern Western Astrologer» by James Braha