creo vs pienso
If I wanted to say 'I think that man is tired' in Spanish, should I say Creo que el hombre está cansado or Pienso que el hombre está cansado? The translation section of this website told me creo, but when I looked at the dictionary (same site) I could not understand why it would be used.
4 Answers
It's a matter of to believe (creer) and to think (pensar).
I believe that the man is tired. I think that the man is tired.
To me, the first implies a firmer decision in your own mind, more of a sure thing. That's just a personal opinion though. 
As Delores says, "creer" is a belief, such as "Creo que vamos mañana." (I think/believe we are going tomorrow).
On the other hand, "pensar" is using your mind, such as when you say "Pienso muchas cosa durante el día." (I think many things during the day).
Along the lines suggested by Marianne, 'creer' has to do with belief. It comes from the Latin "credo, credere, etc.) and is related to the English "creed", "credence", etc. The only English cognates that occurs to me (off hand) for "pensar" is "pensive".
In some societies the distinction can be related to body parts. You 'pensar' with your brain/mind while you 'creer' with your 'heart'/'gut'. 'pensar' is all about (what traditional philosophers would call 'ratiocination' . Decartes gives us "Je pense, donc je suis." (or, in the original Latin, "cogito ergo sum."). This, most emphatically, does not mean "I hold opinions/beliefs.". It is, if anything, closer to "I am a rational being who is capable of (and does) reasoning about ..."
Modern languages (at least, the ones that I have some familiarity with) tend to be rather 'sloppy' about maintaining the distinction. In English 'believe' is generally used in the traditional sense ('hold as a matter of faith') but 'think' is used quite indiscriminately. In Japanese, 'shinjiru' usually corresponds to 'creo' and 'omou' to 'pienso' (but not always). The French 'je crois' and 'je pense' have most of the same problems as do "creo' and 'pienso', which is to say, the distinction is often 'muddied'.
P.S. It is much easier to 'believe' than to 'think'.
You can also say, "se me hace que ese hombre está cansado" (more everyday talk) se me hace: I think, I believe.
