However, many semantic information-oriented applications like Question Answering, Information Extraction and Paraphrase Acquisition require a tighter similarity criterion, as was also demonstrated by papers at the recent PASCAL Challenge on Recognizing Textual Entailment (Dagan et al., 2005).
all these applications need to know when the meaning of one word can be inferred (entailed) from another word, so that one word could substitute the other in some contexts.