Seriation is a process which involves the arrangement of a series of objects following a hierarchical order. An example would be organizing objects by size or alphabetical order.
According to psychologist Jean Piaget, this process is acquired by children in their <u>concrete operational stage</u>, and it's important for understanding abstract concepts such as mathematics and time.
The answer is a high level of commitment to their relationship. This means a deeper level of understanding and a mutual plan of staying together for the rest of their lifetime. Cohabitation is believed to be a sign of high level of commitment.
