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How does knowledge of real-world events shape our understanding of incoming language? Do temporal terms like ‘before’ and ‘after’ impact the online recruitment of real-world event knowledge? These questions were addressed in two event-related brain potential (ERP) experiments, wherein participants read sentences that started with ‘before’ or ‘after’ and contained a critical word that rendered each sentence true or false (e.g., “Before/After the global economic crisis, securing a mortgage was easy/harder”). The critical words were matched on predictability, rated truth-value and semantic relatedness to the words in the sentence. Regardless of whether participants explicitly verified the sentences or not, false after sentences elicited larger N400s than true-after sentences, consistent with the well-established finding that semantic retrieval of concepts is facilitated when they are consistent with real-world knowledge. However, even though the truth-judgements did not differ between before- and after sentences, no such sentence N400 truth-value effect occurred in before-sentences, while false-before sentences elicited an enhanced subsequent positive ERPs. The temporal term ‘before’ itself elicited more negative ERPs at central electrode channels than ‘after’. These patterns of results show that, irrespective of ultimate sentence truth-value judgments, semantic retrieval of concepts is momentarily facilitated when they are consistent with the known event outcome compared when to they are not. However, this inappropriate facilitation incurs later processing costs as reflected in the subsequent positive ERP deflections. The results suggest that automatic activation of event-knowledge can impede the incremental semantic processes required to establish sentence truth-value.