Conjugal Visits

There has been a question brewing in English for quite some time as to why we conjugate only third person singular in Simple Present Indicative cases. One of the reasons that this question has been posed over the years is that English has syncretized over the centuries as it has gone from Old English to Middle English to Early Modern English to Present English. The diachrony of English is hard to explain, but below is a conjugation of the verb "to climb" as it existed in Middle English. In parentheses is the modern day conjugation of the verb "to climb":

MIDDLE ENGLISH SYNTAX (AD c1066-c1500)

Infinitive
clīmben (to climb)

Indicative: present
1 sg
clīmbe (I climb)
2 sg
climbst (You climb)
3 sg
climb (He climbs)
1 pl
clīmbeþ (We climb)
2 pl
clīmbeþ (You climb)
3 pl
clīmbeþ (They climb)

Indicative: past
1 sg
clǭmb (I climbed)
2 sg
clǭmbe (You climbed)
3 sg
clǭmb (He climbed)
1 pl
cloumben (We climbed)
2 pl
cloumben (You climbed)
3 pl
cloumben (They climbed)

Subjunctive: present
1 sg
clī̆mbe (I climb)
2 sg
clī̆mbe (You climb)
3 sg
clī̆mbe (He climb)
1 pl
clī̆mben (We climb)
2 pl
clī̆mben (You climb)
3 pl
clī̆mben (They climb)

Subjunctive: past
1 sg
cloumbe (I climbed)
2 sg
cloumbe (You climbed)
3 sg
cloumbe (He climbed)
1 pl
cloumben (We climbed)
2 pl
cloumben (You climbed)
3 pl
cloumben (They climbed)

Imperative
2 sg
clī̆mb (climb)
1 pl
clīmbeþ (climb)
2 pl
clīmbeþ (climb)
3 pl
clīmbeþ (climb)

Participles
Present participle
clīmbinde (climbing)

Past participle
ȝecloumben (climbed)*circumfixed

In Early Modern English (c1476-c1700), there were only two conjugations that had survived the metamorphosis—second person singular, "thou", which took an -[e]st ending and third person singular, which took an -[e]th ending—and by this time, "thou" was becoming anachronistic in the speech and writing. At this time in history as it also exists today, the present subjunctive would drop the conjugative suffixes and just keep the bare stem of the verb; therefore the present indicative would be, "he doeth/doth" and "thou doest/dost", but in the present subjunctive, it would just be, "he do" or "thou do".

There is no real reason why we still conjugate third person singular present indicative and no real reason why it has evolved from an -[e]th to an -[e]s conjugation. The only thing one can conclude is that the pronouns, "he/she/it" have not changed since the metamorphosis of 2nd person singular so there would be no real reason why it would disappear from the language.

The theory of how the 2nd person singular form disappeared is predicated on the fact that the 2nd person plural had already syncretized centuries earlier. During this time, "ye" was the subject and "you" was the object of the 2nd person plural and there was no conjugative change so one would say, "ye do it" or "I love you".

When the objective pronoun, "you" usurped power from the subjective pronoun, "ye" so that it could exist in both instances, it then made its way into usurping power from 2nd person singular, "thou" to form Modern English's version of an equal 2nd person singular and plural syntagm. Since the new subjective pronoun, "you" now had power, it eviscerated the 2nd person singular conjugation for its own construction, which had been the present subjunctive conjugation of 2nd person singular, "thou".

As for third person singular present indicative, it really is amazing that it has survived. It is the last inflectional verbal base in a conjugative system that syncretized many centuries ago. Will it still exist one hundred years from now or two hundred years from now? Well, the answer to this question is unclear because there are many native speakers who have started to syncretize this construction in their everyday speech when it clearly should be in the present indicative. One can only answer by saying that that's how language works in a nutshell—it evolves, or sometimes, it devolves to a uniform state as has English over the last one thousand years.

With that said, one thing is for sure—it has weathered the test of time for more than a thousand years so it's possible that it may evolve in the future, but there's a very good chance that people will still be conjugating third person singular verbs in the present indicative tense a thousand years from now.