Use information from the following (or your own research) and come up with an answer. First, here are a few search terms to help you get started:
1) Aristotle (a famous philospher, thinker and historical figure) contemplated the same question many many centuries ago. Google the following search terms for some information on his thoughts and do you think they are still relevant today? a) five aristotelian measures of a good money b) aristotle economics
2) Gresham's law is attributed to Sir Thomas Gresham (1519–1579) but the history books report the theory was present many many centuries before him as well. Google "Gresham's Law" and read.
Then decide whether you believe there is such a thing as "good" money and "bad" money as both Aristotle and Gresham state.
The "money" in the U.S. is the "dollar" correct? So, what exactly is a "dollar"? While you may snicker at such a silly question the answer will very likely surprise you. The word "dollar" was in existence even before the country was. The "U.S. dollar" was established to both work alongside the already existing Spanish dollars in current usage in the colonies and with the goal to eventually replace them. Think about it – the only expense to converting all the Spanish dollars into U.S. dollars would be for melting them down and restamping them with the mint markings of the U.S. mint.
A great resource – Historical roots – Google "Edwin Vieira, Jr. dollar" for a number of great articles and videos. Dr. Vieira is an attorney, has argued cases successfully before the US Supreme court and holds four PHDs.
Modern U.S. events:
Google "florida bitcoin case" shows a Florida judge ruled it was NOT money.
Federal Judge rules Bitcoin IS money – https://www.cryptocoinsnews.com/bitcoin-money-rules-u-s-judge-coin-mx-case/
IRS rules Bitcoin is "property" https://www.irs.gov/uac/newsroom/irs-virtual-currency-guidance
FinCEN rules bitcoin is money – http://www.coindesk.com/fincen-rules-commodity-backed-token-services-are-money-transmitters/
Bitcoin is money, U.S. judge says in case tied to JPMorgan hack http://www.reuters.com/article/us-jpmorgan-cyber-bitcoin-idUSKCN11P2DE