J. David Stein divides financial opportunities into three categories based on the likelihood of the financial outcome: investing, speculating, gambling. Investing has a high likelihood of a positive return, speculating has a very uncertain return, and gambling has a high likelihood of negative return. Another common aspect distinguishing investment and speculation is that an investment often yields a positive cash flow and a speculation does not.
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Benjamin Graham in The Intelligent Investor describes an investment as having a reasonable return over a long period of time, while a speculation is a hope for a large return over a short period of time.
