请教下文中短语be committed to的意思

The properties version of the contradiction--a natural extension of the classes or sets version--raised serious doubts about whether one can be committed to objective existence of a property or universal corresponding to every specifiable condition or predicate.
这是有关罗素悖论的一段讲述，大家不必注重其具体内容，能说清楚这里的commit是什么意思即可，多谢！
再看以下这句，好象与大家所说的不是很相符：
We need a theory of reference that renders the sentence 'Polar bears are white' meaningful and true and the sentence 'Unicorns are black' meaningful and false, and yet does not commit us to the existence of unicorns.

请教下文中短语be committed to的意思 be to blame短语中为什么blame不用被动?? 解释短语:be placed on be able to 的短语 be pretty clear about sth. 这个短语中pretty和clear是什么词？什么意思？ 请教：如何在3DMAX中做出光影效果？（请仔细看下文） 请教一个短语翻译. 请教一个短语 请教一下介词短语 请教几个英语短语。