为什么烟叶可以吓退蚂蟥，辣椒可以吓退哺乳动物，茄科植物是有啥魔法吗？Therefore 'are either of you free?'need to usually be correct. Even so 'Is either Peter or Paul free?'can be correct, considering that either is the other of 'both equally' and hence the conjugation 'is' might be correct in these kinds of instance.