 Larson (1988) offers a generative Essentialist approach to the syntax of double-object clauses. In order to provide even a rough outline of his proposals, it will be very useful to be able to use tree diagrams of syntactic structure. A tree is a mathematical object consisting of a set of points called nodes between which certain relations hold. The nodes correspond to syntactic units; left-right order on the page corresponds to temporal order of utterance between them; and upward connecting lines represent the relation ‘is an immediate subpart of’. Nodes are labeled to show categories of phrases and words, such as noun phrase (NP); preposition phrase (PP); and verb phrase (VP). When the internal structure of some subpart of a tree is basically unimportant to the topic under discussion, it is customary to mask that part with an empty triangle. Consider a simple example: an active transitive clause like (Ai) and its passive equivalent (Aii).