Why are both "ye" and "you" used as subjects in Anne Bradstreet's To My Dear and Loving Husband?

As far as I know, in Middle English and Early Modern English "ye" was used for subjects and "you" for objects. Yet in "To My Dear and Loving Husband" by Anne Bradstreet they are both used as subjects in one line: "Compare with me ye women if you can". Why is that? My guess is that in the case of "ye" it is used as a vocative, while "you" is a nominative.

Solution 1:

I think it's right to interpret "ye women" as a vocative phrase in that poem (which explains why the edition that you link to punctuates it with surrounding commas: ""Compare with me, ye women, if you can").

You're also right that ye was originally a subject pronoun, you the corresponding object pronoun. But in Early Modern English, the two forms got pretty confused. Either ye or you could serve as either nominative or vocative, or even accusative, according to the English Grammar of Eduard Adolf Maetzner (translated by Clair James Grece, 1874):

The nominative (also vocative) of the plural ye has in Modern-English yielded to you. John Wallis still cites yee as the nominative, but in the polite address lets you alone pass. Alexander Gill gives, as the nominative and vocative ye and you, as the accusative, you. You was in the first case used only emphatically, especially in Spenser. In common life, as well as in poetry ye still continues alongside of you: And you, the brightest of the stars above, Ye saints ... Be witness (Rowe). Were you, ye fair, but cautious who ye trust (id.). Descend, ye nine! descend and sing (Pope). Ye may no more contend (Longfellow).

[...]

In literature even the interchange of the oblique case you with ye is widely diffused: A south-west blow on ye! (Shakspeare Temp). Vain pomp and glory of the world, I hate ye (id.). Heav'n guard ye all (Otway). [...]

(page 293)

So I wouldn't necessarily assume that Bradstreet consistently used ye for vocative and you for nominative. She does seem to be fond of using ye in vocative contexts though.

I'm looking through this edition of her poems now and tallying the usages of you and ye that I find.

• Ye nominative: "both ye and all men know" (Fire), "how do ye shake" (Earth)

• Ye vocative: "ye high flown quills" (Prologue), "ye martialists", "ye husbandmen", "ye cooks", "Ye Paracelsians", "ye silversmiths", (Fire), "Ye Galenists", "Ye mighty kings", "Ye greedy misers", "ye artificers", "ye affrighted wights", (Earth) "Ye forging smiths", "Ye mariners", (Air)

• You nominative: "if e'er you deign" (Prologue), "you see", "if e'er you made", "you may see", "may you see", (Fire), "you could claim", "where got you ship and sail", "you will see", "if aught you have", "when once you feel me", (Earth), "though you love", "you know to excel" (Air)

• You vocative: "and you, philosophers" (Fire), "hark you, wealthy merchants" (Earth),

• You accusative: "I help you" (Fire) "short of you", "surpass you all", "to tell you of", "calls you forth", (Earth), "what one of you", "speeds you to your port", "heat doth cause you faint" (Air)

It looks like your guess is largely correct, with some occasional variations in usage.