grammar - Art cold? To what extent can pronouns be dropped in English?

Many European languages conjugate their verbs, thus:

I am
You are | Thou art
She is
We are
You are
They are

The form of the verb changes, depending on the person. In some languages (Latin and Polish, to my knowledge), the verb form is completely different for each person, which means that the actual pronoun can be omitted. (I believe it can be reinserted for emphasis.) English can't do that. For regular verbs, only the third person singular has a distinct form. We always use pronouns (except when we don't).

However, in King Lear, at one point Lear turns to his Fool and asks him, "Art cold?" This would not be possible in current English, as the pronoun thou has all but vanished. Was it possible in actual speech in Shakespeare's time, or could it exist in the play only as a poetic flourish?

Answer

Yes, this was ordinary colloquial English in Shakespeare's day, although you was rapidly passing thou. Here are three more instances from Lear:

Art of this house?
Art not asham’d to look upon this beard?
What, art mad?

There was also a contracted form in the indicative:

As th’art a man, Give me the cup. —Ham
Well said; th’art a good fellow —2HIV
Th’art a tall fellow; hold thee to that drink. —TS

An interesting fact (although only marginally relevant to your question) is that Elizabethan/Jacobean English was as likely to contract the pronoun as the verb be. Our it’s appears as ‘tis, our you’re appears as y’are, and our he’s appears as ’a’s—indeed, ’a is the ordinary unstressed form of he:“’a babbled o’ green fields”. (And as often as not, the apostrophes are missing in the printed texts, which can be disconcerting.)