Yi/yijing is similar to already in English. While already frequently occurs in perfect constructions, this adverb alone can signal current relevance, as evidenced by the possible substitution of the perfect of result with the simple aspect taking already in American English and some dialects of British English. Like its English equivalent already, yi/yijing in Chinese can signal the current relevance of a situation.
The current relevance denoted by yi/jing is made clear by the contrast in the following pair:
English: He studied the state’s PE programs for two decades.
An activity taking -le is reasonably expected to be presented as a whole, including its final temporal endpoint provided by a delimiting device. For example, the attested example (a) has a closed reading, indicating that he is no longer involved in that study. To indicate the contrary, the combination of the actual -le and the change-of-state (COS) le must be used, as in the modified alternative (c). In the alternative translation (b), only the actual -le, instead of its combination with the COS le, is used. Yet the sentence still has an open-ended reading rather than the expected closed reading as in (a). This is because the adverb yi is used in (b). As noted earlier, yi/yijing signals the current relevance of an actualised situation. As an activity does not have a final spatial endpoint, its current relevance is only related to its persistence up to the present. As such, when yi/yijing is used, its current relevance reading overrides its actualisation reading. This also explains why these adverbs appear very frequently in aspectually unmarked sentences with perfect meanings.
On the other hand, the adverb ceng/cengjing “once, ever”, when used either alone or in combination with -guo, indicates that an event once happened or a state once held and strengthens the force of experientiality.
As such, 我已去过长城了， 不想再去了。is more natural than 我曾经去过长城，*不想再去了。- 不想再去了 is an instance of current relevance, which is in conflict with experientiality 曾经去过.