-li (podmínková věta)

The enclitic -li functions as a subordinating conditional conjunction meaning "if". It is equivalent to jestli, jestliže, pokud, or když, but it belongs to a highly formal, literary, and administrative register. You will frequently encounter it in legal documents, academic texts, and journalism, but rarely in casual speech.

Strict Grammatical Rules:

• Attachment: It almost always attaches to the verb (either the finite verb or the past l-participle), or to modal predicatives functioning as verbs (e.g., lze-li). A highly common exception is the fixed phrase ne-li (if not / or even), which attaches to the negative particle.
• Syntax: The word it attaches to must be the first word of the dependent clause, though coordinating conjunctions (like a or ale) can precede it (e.g., A bude-li pršet...). You cannot put a subject or adverb before it.
• Clitic Order: Because -li is an enclitic, other Czech clitics (like se, si, mi, ho, by) must immediately follow the verb-li complex in their standard order (e.g., Podaří-li se mi to...).
• Conditional Mood: When used with the conditional, it attaches to the l-participle, which is then followed by the conditional auxiliary (e.g., Měl-li bych čas... = If I had time...). Note: This construction sounds somewhat clumsy and heavy. Even in highly formal texts, it is overwhelmingly preferred to use kdyby for unreal conditions.
• Future Conditions: Unlike English, which uses the present tense for future conditions ("If it rains..."), Czech requires future meaning. For imperfective verbs, this means using the future tense (e.g., Bude-li zítra pršet..., not Prší-li zítra...). For perfective verbs, you use their present morphological form, which inherently expresses the future (e.g., přijde-li).
• Negative Conditions: To form a negative condition, the negative prefix ne- attaches to the verb normally, and -li is appended to the very end of the negated verb (e.g., Neprší-li, Nebude-li pršet).
• Orthography: It must be attached with a hyphen with no spaces on either side (e.g., bude-li).
• Punctuation: Standard comma rules for subordinate clauses apply. If the -li clause comes second, you must place a comma before the word it attaches to (e.g., Přijdu, bude-li hezky.).

Common Confusions:
The exact same structure is used for formal indirect questions meaning "whether" (e.g., Nevím, přijde-li. = I don't know whether he will come). While the form is identical, the grammatical function is an object clause rather than a conditional one.

Beware of Hypercorrection:
Native speakers and learners alike sometimes mistakenly add hyphens to fixed words ending in "li". Words like zdali (whether), neboli (or/alias), čili (so/thus), and ačkoli (although) are single, lexicalized words. They never take a hyphen.