Philo & Sophia · Lesson SixModal verbs: deduction, permission, ability, obligation and advice · B1–B2

How Sure, How Allowed, How Obliged

In which an ink jar shatters, Marcos stands accused, and the library discovers that a handful of small verbs are doing four entirely different jobs at once.

"The ink jar's shattered," Philo said, "and someone has ruined the fair copy of the register."

"Then we'll need every modal verb we own," said Sophia — "for how certain we are, what's allowed, what anyone was able to do, and what anyone owed the library."

How sure — a ladder of deduction

The same word can guess at a fact instead of demanding a duty

"Marcos was sitting at that desk all morning," Demetria said. "He must have done it."

"Wanting it to be true doesn't make it certain," said Marcos.

"She's not accusing you of a duty," said Sophia. "That's a different must. This one marks near-certainty — the evidence points so strongly one way that no other explanation seems possible."

"Deduction, not obligation," said Philo. "The same word, two different jobs."

"It can't have been the scholar," the clerk offered — "he was cataloguing in the east wing since dawn." "Can't have is the mirror of must have," said Sophia — "not impossible in fact, just impossible given what we know." Between those two poles sits a whole middle rung of maybe: "it might have been the wind," "it could have simply fallen on its own," "it may have been simple carelessness" — three different words for the exact same shrug.

"There's your ladder," said Sophia: "must have at the top, might have, could have, and may have in the middle, can't have at the bottom. None of them tell you what happened — only how sure the speaker is. And you needn't use a modal at all: it's likely, I'd assumed as much carry the same weight in plainer clothes."

May and can — two kinds of permission

One word can guess at a fact and grant a favour on two different days

"May I at least examine the desk before you condemn me?" Marcos asked.

"You may," said Sophia. "But you may not touch the ink until Philo has looked at the spill."

"Notice may there is permission, not possibility," said Philo. "It has nothing to do with how sure anyone is — only with what's allowed. That's the same word from a moment ago — there it guessed at a fact, here it grants one."

"Whereas can usually asks whether you're able," said Sophia. "People blur the two, but the library doesn't. And when a modal can't stretch far enough — may has no future — we borrow be allowed to instead: you will be allowed to leave once the ink has dried."

Could versus was able to — ability, general and specific

A standing skill is not the same claim as one particular attempt

"I could always talk my way out of worse than this," Marcos said.

"That's a general ability, true across many days," said Sophia. "It doesn't tell me whether you managed it this time."

"Nobody was able to explain why the wind chose that exact hour," the clerk admitted. "There's the difference," said Sophia. "Could claims a standing skill. Was able to claims one particular attempt — or, here, its failure."

Must versus have to — whose rule is it?

Two words for the same strength of duty, from two different sources

"Whoever spilled it must clean it — that's my rule, here and now," said Sophia. "But every scribe also has to report any damaged text to the head archivist. That rule isn't mine; it's the library's."

"Same strength, different source," said Philo. "One obligation you're choosing to set. One was already written down before you arrived."

Mustn't versus don't have to — two different kinds of nothing

One closes a door; the other simply never locked it

"So Marcos mustn't leave until this is settled?" Demetria asked.

"And I don't have to enjoy it, either," said Marcos.

"Careful," said Sophia — "those aren't opposites of the same thing. Mustn't forbids. Don't have to only means the obligation was never there. Your enjoying yourself was never required, and never forbidden."

"One closes a door," said Philo. "The other simply never locked it."

Philo's footnote

"It's worth naming what English is doing here, since Hebrew doesn't do it the same way," Philo added. "Biblical Hebrew has no single family of modal verbs shouldering four jobs at once the way English's must, may, could, and should do. Necessity leans on a separate word entirely. Ability rests on its own verb, yakol. Permission is carried most often by a bare imperative or a permissive clause. And the softened command Sophia calls should has its own dedicated mood, the jussive, built for exactly that gentler shape of instruction. Where English economizes by making one small set of verbs shape-shift according to context, Hebrew tends to keep a distinct word or mood for each shade of feeling. The ambiguity Sophia keeps untangling in this lesson — one must guessing, another must commanding — is a distinctly English problem to have."

Should, ought to, and the softened command

Command, dressed as a suggestion

"With a latch like that, something was bound to go wrong eventually," said Sophia. "And since it was yours to keep, I'm making you replace it yourself — with your own coin, not the library's."

"One predicts, dressed as duty," said Philo. "The other is duty, handed to you by someone else instead of a rule you already carried."

"You should have asked the clerk to watch the desk before you went wandering," the scholar said. "Noted," said Marcos, "for whichever future avoids this exact past."

"Should, ought to, I'd advise — different phrasing, the same shape of advice," said Sophia. "Only the tone changes how gently it lands." "Command, dressed as a suggestion," said Philo. "The gentlest modal we have."

The clerk returned with the truth of it: the shutter's latch was broken, and the ink jar had sat right beneath it. "Then it was never must have at all," said Philo. "It was only ever might have — and now it's simply did." "So I needn't have defended myself at all," said Marcos. "No," said Sophia. "But you should have fixed that latch weeks ago, when I asked you to."

The lesson in a table

For copying out

Written exercises

A. Rank by certainty

Put these four sentences in order, from most confident to least confident.

1. "It could have been the wind."
2. "It must have been the wind."
3. "It can't have been the wind."
4. "It might have been the wind."

B. Must or have to?

Say whether each rule is the speaker's own, set on the spot, or one that already existed before the speaker arrived.

1. "Every scribe has to report damaged text to the head archivist."
2. "Whoever spilled it must clean it up, here and now."

C. Write both obligations

Write one sentence using mustn't (something forbidden) and one sentence using don't have to (something optional), both about a rule at your own house or school.