The Equity Desk has a page where the difference is explained.
For stock speculation is largely a matter of A trying to decide what B, C and D are likely to think – with B, C and D trying to do the same”. – Warren Buffet
“An Investment operation is one which upon, thorough analysis promises safety of principal and an adequate return. Operations not meeting these requirements are speculative” – Benjamin Graham
“Investment is an activity of forecasting the yield on assets over the life of the assets… speculation is the activity of forecasting the psychology of the market” – John Maynard Keynes
Whenever you rely on knowledge and know what you are doing it is termed as investing but Speculation is when you rely on luck and do not know what you are doing.
What do you do? Invest or speculate or do nothing? 
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Its a difficult question which you are trying to address – bugs every ‘investor’ / ‘speculator’!!
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