Conditions with Nisi, Sin, Dum, and Modo

Latin has more than the basic connector sī “if.” Nisi sets up a negative condition or exception, sīn introduces a contrasting alternative, and dum, modo, or dummodo can impose a proviso: “provided that,” “so long as.” These words do not all select one mood. Nisi and sīn inherit the mood appropriate to the kind of condition, while proviso dum/modo/dummodo regularly takes the subjunctive in neutral or formal Classical prose.

That distinction matters more than the English translation. “Unless,” “but if,” and “provided that” can all sound hypothetical to an English speaker; Latin mood follows the construction and the speaker’s framing, not the vague feeling of English if. The larger system is mapped in Conditional Sentences: Overview.

A Decision Table

Nisi: “Unless” and “If Not”

Nisi generally negates the condition as a whole. It can introduce an open condition with the indicative, a future condition with a future indicative, or a counterfactual condition with the appropriate subjunctive.

The first pluit is present indicative because the weather is an open present fact. The future erit belongs to a straightforward anticipated condition. The imperfect subjunctives adiuvārēs and possem construct a present counterfactual. Nisi does not itself decide among them.

Sī nōn overlaps with nisi, but it is preferable when nōn focuses a particular constituent or forms an explicit contrast.

Here the contrast is today, not tomorrow, so separate sī nōn makes the scope visible. After a negative main statement, nisi can also introduce an exception: nēmō vēnit nisi Mārcus, “no one came except Marcus.” This exception use is neutral Classical prose, but it is not a complete two-clause conditional period.

Fixed turns such as nisi forte and nisi vērō, “unless perhaps / unless indeed,” can introduce a sarcastic exception (formal or rhetorical). Their irony comes from context, not from a new verbal paradigm.

Sin: The Alternative Branch

Sīn is historically and functionally “but if.” It normally follows a stated or easily recovered first condition and opens the alternative branch. Beginning an isolated sentence with sīn without any contrast leaves the reader waiting for the missing first option.

The imperatives and futures in the apodoses are chosen for their own force. Sīn merely marks the second branch. It can also introduce a different conditional type:

The first branch tests an open fact with indicative est. The second deliberately entertains a supposed case with subjunctives sit and faciāmus. The mood shift is meaningful, not agreement controlled by sīn.

Dum, Modo, and Dummodo as Provisos

As conditional provisos, dum, modo, and dummodo mean “provided that” or “so long as.” They state the limit under which the speaker accepts, permits, promises, or commands the main proposition. In this use they regularly take the subjunctive.

The present subjunctives reddās, maneās, tacēās, and dīcās do not tell the reader that repayment, silence, or secrecy is improbable. The mood is licensed by the proviso construction: the speaker presents a required boundary rather than an independent fact.

The normal negative is nē, as in modo nē and dummodo nē. This resembles the negative of commands and purpose clauses because the proviso concerns an intended or required limit. A plain factual dum “while” is a different temporal construction and normally uses nōn with the indicative: dum dominus nōn adest, “while the master is not here.” Do not import the proviso rule into every occurrence of dum.

The permission in licet is bounded by the proviso. English often says “as long as,” which can be ambiguous between duration and condition. Latin mood helps: indicative dum reports overlapping time; subjunctive dum can impose the proviso.

Register and Emphasis

All four connectors belong to Classical Latin. Nisi and sīn are normal in conversation represented by comedy as well as in polished prose (neutral). Modo often stresses that the condition is the one essential restriction, “if only”; dummodo makes the conditional force especially explicit (neutral or formal). Dum is compact and can be rhetorically forceful.

An authentic Ciceronian attack makes the proviso concrete and rhetorical:

The quotation preserves source spelling without added macrons. In dummodo inter mē atque tē mūrus intersit, present subjunctive intersit states the one limit Cicero will accept: Catiline must remain outside the city wall. The form does not suggest that the wall's position is uncertain; the proviso makes it a required boundary.

Poetry may omit an expected element, and post-Classical authors may broaden indicative uses after proviso words. Those (literary or later) patterns do not overturn the productive Classical prose rule.

Parsing and Production

When you meet nisi, identify its scope, then classify the conditional period from the verbs: open indicative, future indicative, imagined future subjunctive, or counterfactual subjunctive. With sīn, recover the first branch and compare the alternatives. With dum, decide first whether it means temporal “while” or conditional “provided that”; mood and context normally decide. Modo/dummodo plus subjunctive strongly signals a proviso.

When composing, use nisi for a broadly negated condition and sī nōn for a focused contrast. Use sīn only for the second alternative. Use dum, modo, or dummodo plus subjunctive to state a limit, and use nē to negate that proviso.

Common Mistakes

1. Making every nisi-clause subjunctive

2. Using sin without a first alternative

3. Using the indicative in a proviso because it seems likely

4. Negating a proviso with non

Key Takeaways

Nisi negates a condition but does not determine its mood. Sīn opens the contrasting second branch and likewise inherits the mood appropriate to its meaning. Conditional dum, modo, and dummodo impose a proviso and regularly take the subjunctive, with nē for negation. Diagnose the connector’s function before translating its verb.