Cosmology

Vietnamese folk cosmology differs across regions, but generally it believes in the three interconnected realms, those being 1. Thiên (Heaven), home to various deities, immortals and good spirits. 2. Địa (Earth), belonging to the humans, animals and natures. Here, karma, life and death are all decided. 3. Thuỷ Phủ/Âm Phủ (Water/Underworld, the two overlap but aren't the same), domain of the water spirits, dead and evil forces. It's ruled by Diêm Vương (Yama), who is the king of hell.

Afterlife

According to Vietnamese folk cosmology, humans have various souls and are divided into two main categories, those being the three souls (Tam Hồn) and the seven souls (Thất Phách). The Tam Hồn are one's spiritual essence and associated with the consciousness and intellect which is reincarnated or ascends after death and exist out of the Thiên Hồn (Heaven Soul) which is given at birth from Heaven, the Nhân Hồn (Human Soul) which is one's actual personality and emotions which may become a ghost or linger near the body after death. The Địa Hồn (Earth Soul), which is one's connection to the body and the phyiscal space and is grounded.

Thất Phách

Now, the Thất Phách are more energetic and unstable than the Tam Hồn and are said to tie in with urges and instinct. In death, they are said to return to nature or just fade away altogether. Because these souls are more unstable, they're seen as dangerous and encouraged to 'tame' or calm through ritual management. There aren't any concrete Vietnamese sources listing the seven, but according to Daoist texts they are pain, lust, anger, joy, affection, fear and craving.

After death

When someone dies their souls undergo a process of judgment, purification and maybe even rebirth. In the first 49 days, one's phách leave but the hồn stays. The soul goes through judgement, carried out by the King of Hell in the underworld while relatives hold ceremonies so the soul will become worthy of reward.

Underworld

The underworld is a type of bureaucratic limbo where the souls are judged based on their karma (nghiệp). Good souls may be either reborn or ascend to a peaceful realm while evil souls face punishment from hell, Địa Ngục. (not the underworld, hell forms part of the underworld. Yama holds the King of Hell title but rules over both the underworld and hell. hell is exclusively for soul punishment.) Yama will then send the soul to one of the Ten Court of Hell, where each court's judge decides the reward or punishment based on the karma.

If a soul is properly honored within the 49 days, the soul may become a protective ancestor (tổ tiên) but if they are wronged the soul may become a restless ghost (ma, oan hồn) who haunts the living. Exorcisms (trừ tà) and rituals (cúng cô hồn) can be practiced to appease these souls, though.