Everybody in the world of the series has three souls in their bodies, which are linked together.
Name Soul - This soul is important when discussing illness. It is said that if you are ill, you shouldn't see your name soul in the water (essentially the reflection), or you will lose it and fall in. This soul tells you who you are and is your personality. The loss of the Name Soul after death results in the creation of a ghost, eternally seeking the clan it has lost.
Clan Soul - This soul tells you right from wrong, and helps to express and suppress emotions. The loss of the Clan Soul after death results in a demon, eternally craving life.
World Soul - Your World Soul stays in the body when spirit walking. The other two souls leave the body to spirit walk. Each World Soul is a part of the Nanuak, and provides a link to the World Soul of every other living thing. The loss of the World Soul after death would result in the creature or person becoming Lost forever in the darkness behind the stars, cut off from every living thing.
After death, when the souls are released from the body to begin the journey to the First Tree, they can become separated. In some creatures, such as wolves, this rarely happens due to their strong senses of smell and hearing, which help the souls stay together. Humans, however, require death marks (ochre circles daubed on the heels for the Name Soul, the breast for the Clan Soul and the forehead for the World Soul) to help the souls recognise each other and not become lost on the Death Journey.
Sometimes, when dreaming or if you are ill, the Name Soul might slip out, and the rest of the body sleepwalks to search for the errant soul. Often, they are reunited before either leaves the shelter.
Souls can also become sick: depending on which soul becomes sick, the person might become something similar to a ghost, a demon, or a lost one. Magecraft is often used to heal sick souls - for example, when Seshru caused Torak's World Soul to fall sick in Outcast, Renn sent him help in the form of the two young ravens, Rip and Rek. Through looking after them, Torak re-established his link with other living things, allowing his World Soul to heal.