What is a Visionary Phrase™?

Question

_{This is in the spirit of the What is a Word/Phrase™ series inaugurated by JLee with his original Phrase™ and Word™ puzzles.}

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If a phrase adheres to a certain rule, then I call it a Visionary Phrase™.

Use the examples below to find the rule.

VISIONARY PHRASES	NOT VISIONARY PHRASES
WHEN SOME WHIR	ONCE MANY PURR
LUST THEN SNOG	SHAG OVER PINE
SOME BOLD JAZZ	ANY OLD POP
BREW NEAR OVEN	STEEP ABOVE STOVE
MINER BURNT LOWRY	DIGGER SPOILT TURNER
KILL HIS DATE	SLAY HER BEAU
VOGUE TOFU CABAL	POSH VEGAN SECT
FETAL RALPH WEEPS	BENT JOHN SOBS
COTTON TIGHTS RUNOFF	SILKEN SHORTS SPILLAGE
SAUCE OR GRITS	GRAVY AND QUESO
OTTO PENS BLUE	JESS JOTS GREY
BLUNT BAKER CLERK	CURT BUTCHER HELP
PINK SWAN DON	GREY SHOE SUE
THE WEAK PLED	FEW ABLE HID
STEAM THREE BONES	BOIL FOUR LEGS

In case you want it in CSV:

VISIONARY PHRASES,      NOT VISIONARY PHRASES
WHEN SOME WHIR,         ONCE MANY PURR
LUST THEN SNOG,         SHAG OVER PINE
SOME BOLD JAZZ,         ANY OLD POP
BREW NEAR OVEN,         STEEP ABOVE STOVE
MINER BURNT LOWRY,      DIGGER SPOILT TURNER
KILL HIS DATE,          SLAY HER BEAU
VOGUE TOFU CABAL,       POSH VEGAN SECT
FETAL RALPH WEEPS,      BENT JOHN SOBS
COTTON TIGHTS RUNOFF,   SILKEN SHORTS SPILLAGE
SAUCE OR GRITS,         GRAVY AND QUESO
OTTO PENS BLUE,         JESS JOTS GREY
BLUNT BAKER CLERK,      CURT BUTCHER HELP
PINK SWAN DON,          GREY SHOE SUE
THE WEAK PLED,          FEW ABLE HID
STEAM THREE BONES,      BOIL FOUR LEGS

Hint 1:

The following are also Visionary Phrases:

Hint 2:

If you've been focusing on formal properties of these phrases, I would suggest shifting to something else; you can also try thinking along the lines of meanings and etymologies.

Hint 3:

Focusing on the first letter should help.

Hint 4:

Hints 2 and 3 are playfully ambiguous.

Hint 5:

Focusing on 'A' should help. In particular, look for a pattern.

Answer 1

I think I'm onto something here ...

The original version of this solution included a lot of unnecessary (but not incorrect) arithmetic. As @Arth suggested, the calculations added up to a Vigenère Cipher. The three words in each Visionary Phrase™ correspond to the ciphered text, plain text and key, in some order.

WHEN SOME WHIR

Using SOME as the ciphered text and WHEN as the key, the plain text is WHIR.

LUST THEN SNOG

Here, LUST is the ciphered text, THEN is the key, revealing SNOG as the plain text.

SOME BOLD JAZZ

BOLD is ciphered, SOME is the key, and JAZZ is the result.

...

PINK SWAN DON

Due to the nature of the cipher, it's not possible for the plain text and cipher text to have different lengths. The outlying word must be the key. In this case DON must be the key, which transforms a ciphered SWAN into PINK.

Those designated as a Non Visionary Phrase™ do not enjoy this relationship.

It's also worth noting that if you squint really hard, Visionary looks like Vigenère, and even shares some sounds.