Comma as a conjunction

We treat comma as a conjunction in conjoined lists. It anchors the same trees as the lexical conjunctions, but is considerably more restricted in how it combines with them. The trees anchored by commas are prohibited from adjoining to anything but another comma conjoined element or a non-coordinate element. (All scope possibilities are allowed for elements coordinated with lexical conjunctions.) Thus, structures such as Tree 22.5(a) are permitted, with each element stacking sequentially on top of the first element of the conjunct, while structures such as Tree 22.5(b) are blocked.

	0.5in
(a) Valid tree with comma conjunction	0.5in	(b) Invalid tree

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This is accomplished by using the <conj> feature, which has the values and/or/but and comma to differentiate the lexical conjunctions from commas. The <conj> values for a comma-anchored tree and and-anchored tree are shown in Figure 22.6. The feature <conj> = comma/none on A₁ in (a) only allows comma conjoined or non-conjoined elements as the left-adjunct, and <conj> = none on A in (a) allows only a non-conjoined element as the right conjunct. We also need the feature <conj> = and/or/but/none on the right conjunct of the trees anchored by lexical conjunctions like (b), to block comma-conjoined elements from substituting there. Without this restriction, we would get multiple parses of the NP in Tree 22.5; with the restrictions we only get the derivation with the correct scoping, shown as (a). Since comma-conjoined lists can appear without a lexical conjunction between the final two elements, as shown in example ((432)), we cannot force all comma-conjoined sequences to end with a lexical conjunction.

(431)0(431

(432)

So it is too with many other spirits which we all know: the spirit of Nazism or Communism, school spirit , the spirit of a street corner gang or a football team, the spirit of Rotary or the Ku Klux Klan. [Brown cd01] 

{$\beta$a1CONJa2 (a) anchored by comma and (b) anchored by and