What are the three qualitative and one quantitative indicators of an asset class?

I mean what are the 4 characteristics that characterize an asset class? For example why are bonds, stocks, TIPS, commodities, FX, real estate considered a separate asset class? I don’t want the differences between these specific asset classes. Just the theoretical bedrock of this definition.

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September 10th, 2010 at 11:19 am
Your best bet for definitions is one of these two
http://www.investopedia.com/search/searchresults.aspx?q=asset+class
http://en.wikipedia.org/wiki/Asset_allocation#Examples_of_asset_classes