The division of English into Old English， Middle English， and Modern English is nonconventional and not arbitrary.

An important difference between presupposition and entailment is that presupposition，unlike entailment，is not vulnerable to negation. That is to say, if a sentence is negated, the original presupposition is still true. 点击查看答案&解析

Linguistic forms having the same sense may have different references in different situations while linguistic forms with the same reference always have the same sense. 点击查看答案&解析