本文探討的議題是今文《尚書》的「惟」字分裂句。過去已有許多研究指出「惟」具有標示信息焦點的語用功能，卻甚少有人從分裂句的角度論究其句式的特點，是以這篇文章的重點即放在「惟」字分裂句的句型分析及其焦點分布。分裂句的「惟」是一個以子句作為賓語的一元動詞，因子句中主語提升與否，表現為單部句和雙部句兩種類型。當主語提升之後，「惟」居謂語之前，則信息焦點便可能是謂語、前置賓語或述語前的狀語；如果主語留置原處，「惟」居句首，則信息焦點又會是整個子句，抑或緊隨於「惟」後的主語、狀語。此外，「惟」不論置於句首或謂語之前，都還可能作為肯定命題之用。最後，本文主張應該正視分裂句「惟」與判斷句繫詞用法之間的差異，兩者不能等同視之。

Much has been done in identifying 惟wei (in 惟wei clefts) as a focus marker, but much still remains to be done to identify the structural properties of 惟wei clefts. It is therefore our goal to attempt a formal description of 惟wei clefts, and to determine the actual scope of the focus marker 惟wei. It is argued that 惟wei is a one-place predicate, taking a clausal complement whose subject can be raised to the matrix subject position, namely the slot preceding 惟wei. With the subject raised, 惟wei precedes the remaining predicate, so the informational focus can fall on the predicate or the adverbial/the preposed object inside the predicate; with the subject in situ, however, 惟wei precedes the embedded clause, so the informational focus can fall on the whole clause or the subject/the adverbial following 惟wei. In addition, regardless of惟wei’s distribution, it may pertain to the assertion of the proposition. Finally, it is further suggested that the copula 惟wei is different from the focus-marking 惟wei.