I believe that ALL memorizing is done by association, but you may not always know what the association is. You may build the association through simple repetition, or you may use a known mnemonic system. The mnemonic system is making the association obvious and known to you. It will be an "artificial" method, but it is still creating a link between something KNOWN and something UNKNOWN. If something is memorized, then you have a mental filing system that allows you to retrieve it.