Really interested to know, from a reliable source, whether or not canceling credit cards has a negative impact on credit score--as well as other basics of credit scoring. Is there a good book or FAQ I can refer to? I realize things change, making books less current; but presumably the basics don't change all that often (?).

Although I've heard people say canceling cards can lower your credit score (here defined as cards one has fully paid off), I'd like to know precisely how and why--if it's even the case. I've heard that, yes:

1) If you're using ~50% of more of your credit line and cancel a card, that can have a negative effect on score

2) If you cancel your cards but don't have any other accounts that have a history of 6 months or greater, that can affect your score. But anyone with a mortgage and good payment history... well, how many damn accounts does one need to keep open to have "good" credit?

And can't your credit actually improve slightly if you cancel card with high limits? e.g. if I cancel two cards with a 15K limit each, I am 30K total less of a risk to other banks?

Also, I can see how applying for too many cards too frequently could result in "too many inquiries in 12 month" denials. But does canceling a card really count as an "inquiry"?

Interested in answers here, but prefer a good book on the subject--something I can have as a reference; or a really good FAQ.