Somers: "On the validity of the complement--adjunct distinction in valency grammar" (1984)

In this article from Linguistics 22(4), Harry Somers surveys various linguistic tests designed to detect the difference between optional sentence adjuncts and obligatory verbal complements. He further proposes to replace this binary distinction by a six-step scale ranging from intergral complements to extraperipherals.

Tests for Argument Type
The most import tests Somers discusses are the elimination test, the back-formation test, and his own "do so" test. Here is an overview of the tests he describes:

• Elimination: If the sentence becomes ungrammatical when an element is eliminated, it is a complement. If it doesn't, then the test makes no conclusion (pp. 509-10).
• Back-formation: If the element can be moved down in an embedded wh-sentence or into a entirely separate sentence, it is an adjunct (p. 511).
• Substitution 1: If the elimination test does not yield a conclusion for a particular verb, but it does for a near-synonym, then we are allowed to transfer the complement status back to the original verb (p. 512).
• Substitution 2: If a change of verbs renders a certain element strange or ungrammatical, then that element is a complement. If it doesn't, no conclusion is guaranteed (pp. 512-13).
• Semantics: If the preposition in a prepositional element cannot be replaced by a near-synonym, then that element is a complement (p. 514).
• for/to status: If an indirect object is most naturally expressed as a to-phrase, it is relatively loosely connected to the verb (although perhaps still a complement); if it is most naturally expressed as a for-phrase, it is a complement (p. 515).
• Questions: If the noun within an element can be referred to with who, whom, or what, it is a complement. If it cannot, it is an adjunct (p. 516).
• "Do so": Whatever elements are semantically included in the referent of the anaphor ...and he did so, too are complements. The rest are adjuncts (p. 516-20).

A Scale of "Complementness"
Somers suggests (p. 524) that we give up the binary distinction between complement and adjunct and instead introduce a six-point scale that measures how intimately connected to the verb any particular element is.

His categories, with examples, are (pp. 524-26):

• Integral complement: put at risk, take care (fundamentally affects the verb).
• Obligatory complement: he wrote me a letter (necessarily implied by the verb).
• Optional complement: Greame caught Steve a salmon (optional, but quite restricted).
• Middle: I gently pushed the button (optional and only weakly thematically restricted).
• Adjunct: I pulled the lever in order to eject (optional and almost unrestricted).
• Extraperipherals: we're all patiently waiting for you, you know. (top-level additions)