首先來介紹一下some的用法：
1、some 與不可數(shù)名詞連用：一些,若干
例句：There's some ice in the fridge.冰箱里有些冰塊兒.You left some money on the table.你把錢落在桌子上了.Please have some cake.請(qǐng)吃點(diǎn)兒蛋糕.
2、some 與復(fù)數(shù)可數(shù)名詞連用,通常指三個(gè)或三個(gè)以上
例句：If you put some pictures on the wall,the room will look brighter.你要是在墻上掛幾幅畫,這個(gè)房間就更有生氣.
3、some 與單數(shù)可數(shù)名詞連用：未知的或未確指的人、地點(diǎn)或事物
例句：Some man at the door is asking to see you.門口有人要見你.She won a competition in some newspaper or other.她參加某報(bào)紙舉辦的比賽獲勝.
所以對(duì)于你的問題的回答是：some可以修飾單數(shù)名詞；肯定、否定句并無硬性規(guī)定.