The present study investigates the L2 acquisition of English psych predicates which pose a linking problem for theoretical linguists and a learnability problem for ESL/EFL learners. Psych predicates assign the theta role of Experiencer to the NP that experiences the emotion described by the predicate. In cases like Small children fear dogs, the Experiencer appears in the subject position whereas in other cases like Dogs frighten small children it surfaces in the object position. In the absence of negative evidence, how do Chinese-speaking learners of English acquire the knowledge as to what determines the mapping of Experiencer into subject and object position?This learnability problem is approached within the generative framework, through a linguistic analysis of psych predicates in light of lexical determinism and Pesetsky’ s fine-grained semantic analysis. The syntactically relevant meaning component that sets psych verbs apart into two different types, and determines their relevant semantic structure is zero CAUS, a covert and phonologically null CAUSE embodied in Object Experiencer (OE) predicates. The analysis shows that the acquisition of psych predicates can boil down to the recognition of this argument-structure-changing morphology zero CAUS in OE verbs and V-ing adjectives (VingAs).Zero CAUS is further examined in the typological framework. A typological causativization parameter is developed on the basis of a cross- linguistic analysis, which demonstrates that English has both lexical and analytical causatives and so does Chinese, arguably. What English and Chinese differ is the canonical setting/value of the parameter lexical for the former and analytical for the latter.The linguistic and cross-linguistic analyses lead to the central research question: What triggers the recognition of zero CAUS in OE verbs and VingAs?A Semantic Salience Hierarchy Model is established to address the question. To assess the plausibility of our model, 9 specific hypotheses about four identified variables, i.e., cross-linguistic influence, a UG component, elements in TL input, and animacy, were investigated using a writing production task and a grammaticality judgement task. 126 learners of three different levels (i.e., elementary, intermediate and advanced), together with 32 native speakers of English, participated in the investigation.The results show that L2 learners gradually developed sensitivity to zero CAUS and reset the parameter as their English proficiency improved. Lower level learners were significantly more accurate on Mutual OE verbs than on Exclusive TL OE verbs, suggesting the influence of a latent causativization rule in Chinese. Within the TL elements, a facilitating effect was found with the overt causative morphology like -en, but an inhibitory effect was found with the further affixation of -ing to the zero-derived OE verbs in VingAs. L2 learners behaved like native speakers in accepting inchoative/stative use of alternating verbs, lending support to their respect of Thematic Hierarchy, a UG component. Higher level learners showed the same tendency as that of native speakers to prefer inanimate Causer over animate ones in both OE verbs and VingAs. All these findings empirically verified the Semantic Salience Hierarchy Model. Furthermore, the IL development demonstrates a clear interaction between the morphosyntactic knowledge of zero CAUS, L1 transfer, UG and animacy.