Discourse markers (DMs, hereafter) have been well explored in the history of English. However, the vast majority of preceding studies on DMs focus on the earlier stages of English (e.g. Brinton 1996, 2008). This study pays attention to the recent development of DMs especially in Present Day English, with special focus on (the) point is, based on The Corpus of Historical American English (COHA, hereafter) and collaterally supplemented by other corpora as needed basis. The main coding property centers on whether the construction (the) point is appears with the complement clause with that (i.e. main clause type) or is unattached from the following clause, accompanied by comma (i.e. DM type); the determiner-headed the point is construction is examined separately from the counterpart point is construction.
The survey results are as follows. The construction (the) point is had been infrequent up until the late nineteenth century, regardless of whether it was an example of main clause or DM. From the end of the nineteenth century, the construction itself began to increase and the main clause type had been dominant over the DM type. However, the main clause type peaked out around 1960s in terms of frequency, with a sudden decline in number in 1990s and 2000s. On the other hand, the DM type has increased mostly steadily to the present, finally becoming dominant in 2000s. Along with the syntactic change from main clause to DM, the construction (the) point is has come to prefer modifier-less and determiner-less expressions, both of which come to terms with patterns of grammaticalization. These discourse-syntactic properties are shared among related constructions such as (the) fact is, (the) question is, (the) truth is, (the) thing is, (the) problem is, (the) reason is, (the) result is, etc., all of which can be viewed as part of (the) NOUN is construction.
One conspicuous difference among these related constructions is whether the speaker’s stance is syntactically reflected or not. For example, in the case of (the) point is construction, the first person possessive construction my point is emerges in 1873 in the corpora. At the very advanced stage of grammaticalization, a given form would have become saturated or oversaturated with pragmatic forces incremented in it, and as a consequence, the form would increase its own spread (morpho)syntactically as well as pragmatically, as in the case of my point is; my thing is and my reason is are found, while *my truth is, *my fact is and *my result is are not. On the other hand, several of (the) NOUN is constructions witness the syntactic reflection of intersubjectivity as evidenced by your question is, your answer is and your problem is. Presumably, the types of nouns in constructions have some bearings on to what extent one construction is grammaticalized, and accordingly, the rate of linguistic change differs from one type of constructions to another. For example, the DM type of (the) point is construction (c. 1750) took more than 120 years to witness the subjective expression my point is (c. 1873), while the DM type of (the) answer is construction (c. 1817) took only 11 years to reach the subjective stage my answer is (c. 1828), linked in a small amount of time i.e. 36 years to the intersubjective stage your answer is (c. 1864). However, the syntactic-pragmatic change follows the general cline of change from subjective to intersubjective, but never the reverse, according to the survey results.
Brinton, L. J. 1996. Pragmatic markers in English. Berlin and New York: De Gruyter Mouton.
Brinton, L. J. 2008. The comment clause in English. Cambridge: Cambridge University Press.