A little background: In some older Semitic languages, including Akkadian, the causative stem (what in Hebrew is the "hif'il" and in Arabic is the form IV أفعل) was characterized by the "sh-" prefix rather than the Hebrew "ה" or Arabic "أ".
This form of creating the causative meaning was then borrowed by Aramaic speakers to create the "shaf'el" binyan in Aramaic. Then Hebrew borrowed this concept from Aramaic, but patterned them as 4-letter pi'el verbs rather than equating them with the hif'il. So essentially the addition of the ש root letter creates a four-letter root with a causative meaning.
Some examples:
- שחרר to free
- שעבד to enslave
- שחזר to return
- שכנע to persuade