gravesville says... #2
100.2a In constructed play (a way of playing in which each player creates his or her own deck ahead of time), each deck must contain at least sixty cards. A constructed deck may contain any number of basic land cards and no more than four of any card with a particular English name other than basic land cards.
In EDH/Commander you can only have one copy of any card other than basic lands.
April 6, 2011 8:51 a.m.
Dual lands are not basic lands. While some of them (Taiga , Godless Shrine and others) might have a land type (forest, swamp etc.), without the supertype 'Basic', they aren't basic lands and thus are subject to the 4-of or 1-of limit for how many of them you may include in a deck.
six says... Accepted answer #1
in legacy they are subject to the 4 of copies like nonbasic lands
EDH you can only have one of everything except basic lands
April 6, 2011 6:56 a.m.