Are you saying the author recommends mixing check with plaid? That combination is known to cause blindness and insanity in lab animals.

Maybe the book was penned in the '70's. Maybe the author was in the plaid racket. Either way, forgive me for saying this, but the author's taste is suspect.

And, yes, some patterns will match with tartan. I can't think of any off the top of my head, but I'm sure they exist. But it's a difficult trick to pull off, and most of us dumb guys probably shouldn't risk it.
Again, not necessairly. The book was written in 2001, and it can be done. It all depends on the colour and size of the pattern in question. Tatersall and Glen Plaid dress shirts work very well with kilts in day/hunting attire. I have a Glen Plaid/Prince of Wales Check dress shirt that goes quite nicely with my kilt. I personally prefer a coloured and/or patterned dress-shirt to the plain, white dress shirt that is always seen with Highland attire, but that's just my style. Doesn't mean that I'm "right".

And there is a historical precdent for "mixing" tartans and patterns; take a look at any print from the Jacobite Rebellion and you will see a wide variety of Scottish gentlemen wearing a kilt in one tartan, hose in another and a jacket in yet another! (I don't know if I would go that far!)

It's really all a matter of individual style. It may not look right to you, but that dosen't mean that it is not right.

Cheers,

T.