Thanks for your question. I was having trouble with the chat interface so I switched to this Q&A format. Feel free to ask follow up questions on the same question until I have answered your question fully.
Certain areas of law are much more about gray area than you'd think, which is why there's differing cases online.
While there's truly no definite answer on some of these questions unless you were to be taken to court and won (or lost), I can give you my definite opinion as to whether any of the following are a good business risk:
1. Movie Quotes: What confuses most people about movie quotes in copyright
is that there are a number of cases where short phrases aren't given copyright protection. But many of these are titles, tag lines, or otherwise not part of the original script/dialogue.
Using a quote, taken from within the context of the movie dialogue itself, if it would be recognizable as part of the whole copyrighted work, is risky ground. If your quotes meet the above standards I would consider them too risky to use on your T-shirts. Putting the movie name or movie art on the shirts would make the case much easier for the owner of the rights as it would clearly tie the quote to the movie. It would also potentially open up trademark
issues for the movie name and additional copyright issues if you took art directly from the movie.
Additionally, if the quote itself was trademarked you'd be liable for trademark infringement
2. Phrases from Popular Books: This would be subject to the same tests above. If the quote was easily recognizable as coming from a specific book you'd be running into risks that are not worth taking.
3. Classic works are a different story if they've entered what's known as the public domain. This means that any copyright once held has now expired. Any work published before 1923 is in the public domain and any or all of it can be used freely without license.
The only exception would be if there was a trademark also associated with the book title or phrase. For example, "Red Fish, Blue Fish" is registered by Dr. Seuss' corporation for some specific classes of goods. Even if the copyright expired the trademark would still be enforceable.
For guidelines on the timing for works published after 1923, check here: http://www.unc.edu/~unclng/public-d.htm