If you have vs if you had
you may consider "倘若", "假如", or "假使"

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000051670

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000089761

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000089751

but, the chinese language is "fuzzy", these terms do not absolutely indicate an untrue condition in the clause; they just merely imply such.