'Propose' is a verb. 'Proposal' is a noun. The tricky part is telling the difference between 'proposal' and 'preposition'. They're both noun forms of 'proposal' and they are often interchangeable, but not always. Even as a native speaker I'm finding it hard to figure out exactly what the difference is. I looked it up and found these: http://forum.wordreference.com/showthread.php?t=1782549 http://forum.wordreference.com/showthread.php?t=843736

propose : to offer or suggest for consideration, acceptance or activity. - to propose a new method. - to offer (a toast) . - to suggest. - to present or nominate for a position.- to put before oneself as something to be done; design; intend. Proposal is the same thing. Just you use this word when asking in marriage