To use the term blind faith, is to use an adjective needlessly.
I had heard the above quote from a positivist friend some time ago. Also, the dictionaries define "faith" as a "belief that is not based on proof" or an "unreasoned belief".
So my question is: Is "faith" by definition "blind"? If no, what is the difference between mere "faith" and "blind faith"?
Billare's comment on the question provides most of the answer. To go a bit further, "blind" is indeed a intensifier and can be used to modify "faith" in this way.
However, we can also posit degrees of faith. A "reasoned faith" would be belief with some measure of logical or evidential support.
"Blind faith" would be faith with no reason, and conceivably faith in spite of evidence to the contrary. The term normally arises in reference to the latter type, and is slightly pejorative.
"Faith" in my dictionary is:
complete trust or confidence in someone or something
This has no implications on proof or otherwise. For instance, I have faith in gravity. "Blind faith" is classifying "faith" to mean "faith without evidence or proof." Your friend's quip is mostly a comment on the common usage of "faith" as implying "blind faith" and is intended as a jab at people who take their (albeit blind) faith extremely seriously.
The differences between faith & blind faith are simple. Faith is believing in something; with or without any information about whatever that something is. Blind-faith... is lacking in some component(s) of information but still continuing to believe in something.
Similar to devotion and blind-devotion.
You can have faith that something will occur knowing that the evidence suggests the outcome... but blind-faith is having faith something will occur with no evidence or conflicting evidence against that outcome.
I have faith that my car will start in the morning, in the sense that I assume it without thinking. But it's not blind faith, because I know roughly what is supposed to happen, and might even be able to fix a simple problem. My faith in a computer, however, is blind: for all I know there may be a small demon trapped inside each one (come to think of it, that would explain a lot...). Note that no knowledge of programming will change this last point: I would need among other things, a soldering iron to convert my faith into a rational belief.
I think "faith" has a positive to neutral connotation, whereas "blind faith" has a more negative connotation.
Faith is not blind, but belief (sometimes hope) in something one cannot know: the nature of God, the future outcome of some event, even in the power of scientific discovery to illuminate anything we can observe. People will say they have faith in one of these things.
A person will generally not declare they have blind faith. Others are more likely to attribute it to them. I agree with @Billare it can act as an intensifier, as it might suggest someone's willful ignorance. Depending on context, it might also refer to someone to who believes in something without foundation for the belief itself, or faith for it's own sake.
Faith is something you have hope or belief based on your own experience and from the experience of others. Also by logical thinking.
Blind faith is much stronger, that you hope or believed whatever is happening or will happen even in contrary to your reasoning. A man save up money for his life time work.
Then finally on his old age, he has enough money to start building a small church. Before the church was completely done, the church burns to the ground with faulty electrical wiring.
Why will God alow the church to burn? After all, this is not for the man but to serve and worship God. The man has blind faith: he does not know the reason, but he chooses to believe in the goodness and power of God, and to still worship God.
