'Propose' and 'purpose' are surprising doublets — both from Latin 'proponere' (to place forward).
To put forward a plan, suggestion, or idea for consideration; to nominate someone for a position; to make an offer of marriage.
From Old French 'proposer' (to put forth, to suggest), a Romance remodeling of Latin 'prōpōnere' (to set forth, to put forward, to display), from 'prō-' (forward, before, in front of) and 'pōnere' (to put, to place). The literal meaning is 'to put forward' — to place an idea or plan before others for their consideration. The marriage sense appeared in English by the 18th century, from the more general
The English word 'purpose' is a disguised doublet of 'propose' — both descend from Latin 'prōpōnere,' but 'purpose' arrived through an Old French form 'purpos' that had drifted far enough in sound and meaning to become unrecognizable as the same word. To have a purpose is, etymologically, to have something 'placed forward' as an aim.