Attachment takes place during a sensitive period (up to 2.5 years). The child forms an attachment which is qualitatively the same than other attachments this is called monotropy. This primary attachment provides a secure base to which the child can return when frightened.
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The primary attachment also provides a template which the child uses to guide future attachments, continuity hypothesis.
Therefore there is a link between childhood attachment and adults relationships (internal working model).
Bowlby argues that failure to develop warm and continuous relationship with a caregiver during the critical period (6-9 months)