针对二语形态的默认问题，McCarthy 提出了形态不充分赋值假设。本文介绍该假设内容，思考其贡献与不足，并通过一项对中国西班牙语学习者口语语料中性数使用的研究， 对假设进行检验。研究结果支持假设对默认形式是不充分赋值形式、 学习者主要产出不充分赋值错误的论断，但不支持它对学习者避免特征冲突错误的预测。

For the issue of defaults in L2 morphology， McCarthy proposed Morphological Underspecification Hypothesis．This paper introduces the MUH， thinks about its contributions and shortcomings， and tests it by a study on the gender and number in spoken Spanish by Chinese Spanish learners． The results support the assumption of MUH that defaults are underspecified forms， and L2 learners produce primarily underspecification errors， but contradict its prediction that learners avoid feature clash errors．