The syntactic constraint function penalizes ungrammatical parses by encouraging the semantic parser to produce parse trees that agree with a dependency parse of the same sentence (Krishnamurthy and Mitchell, 2012; Krishnamurthy and Mitchell, 2013;Krishnamurthy and Mitchell, 2015).
the syntactic constraint requires the predicate-argument structure of the CCG parse to agree with the predicate-argument structure of the dependency parse.