What does a "lukewarm" letter of recom usually mean?

[NBZ]

If you are going to write that kind of letter, it is really better just to refuse to write one in the first place. Perhaps that professor may have thought, "But the point of the recommendation system is to provide honest and unbiased assessments." Maybe, but the vast majority of such assessments (I suspect) are truncated below at the level of "This is a competent candidate who is diligent and has shown good aptitude for coursework." So if you're going to go below that, it's going to send a massive negative signal. The adcoms are not just going to think that the candidate "will likely not succeed" (that is after all true for many people), the adcoms will think "this candidate has absolutely no chance of succeeding."

[Mathew952]

Honestly, from when I spoke to the Adcom/Professors at my school, They said that generally a lukewarm letter shows that the professor really has nothing substantive to say. The grade you got is on your transcript, and Econ Adcoms know what's covered in Intermediate Micro. They said the important thing is some *specific* information about your skills, about your talents, passion, work ethic- Not just "he's a hard worker" but something like "he put in close to 50 hours a week working on this project with me, met every deadline, and exceeded my expectations". Vague letters, even letters of strong praise, are inferior to detailed letters.