откад / од када / од тада

1. Function and Syntax

Откад (along with its variants откада and од када) connects an initiating event or baseline condition to an ongoing or subsequent state. It corresponds to English 'since' or 'ever since'.

The conjunction откако can also be used as a synonym for откад, but only when introducing a subordinate temporal clause (e.g., Откако живим овде...). Unlike откад / од када, откако cannot function as an interrogative adverb to ask questions (e.g., *Откако си овде? is incorrect; you must ask Откад си овде? or Од када си овде?).

Од тада (or the fused form отада / отад) is a demonstrative adverb meaning 'since then'. In complex sentences, the two can form a correlative pair: Откад..., [од тада]..., although од тада is optional in the main clause and serves primarily for emphasis.

2. Sound Changes and Orthography

Pay close attention to standard orthographic rules regarding fused versus split forms:

• Voicing assimilation (једначење сугласника по звучности): In the fused variant, the voiced dental д in од becomes voiceless т before the voiceless stop к: од + кад → откад (or откада). Writing *одкад is incorrect.
• Simplification of consonants (губљење сугласника): In the fused variant of од + тада, the two identical dental stops simplify: од + тада → *оттада → отада (or отад). Writing *одтада or *оттада is incorrect.
• Split vs. fused spellings: According to the normative standard, split spelling is permitted only when using the full form ending in -а: од када and од тада. The shortened forms lacking -а must always be written fused: откад and отад (spellings like *од кад and *од тад are orthographically non-standard).

3. Tense Harmony: Present vs. Past

Unlike English, which uses the present perfect for an ongoing action that began in the past ('I have lived here since...'), Serbian uses the ordinary present tense when the state continues into the present moment:
• Откад живим овде, боље се осећам. (Ever since I've been living here, I feel better.)

Tense combinations across the clauses depend directly on the time frame and the nature of each event:

• Completed initiating event with ongoing result: When the subordinate clause denotes a punctual, completed starting event, it takes the past tense (перфекат), while the main clause remains in the present if the resulting state continues now: Откад се доселио, све је другачије. (Ever since he moved, everything is different.)
• Non-occurrence since the starting point: When stating that an action has not happened at all since the baseline event, the main clause requires the negated past tense: Откад су завршили школу, нису се видели. (Since they finished school, they haven't seen each other.) / Откад је отишао, нисмо се чули. (Since he left, we haven't spoken.)
• Past periods: If the entire situation unfolded in the past and does not extend to the present, both clauses use the past tense.

4. Important Distinctions

• Strictly temporal: In English, 'since' can mean 'because' (e.g., 'Since it is raining, stay inside'). In Serbian, откад is never causal. For reasons or causes, always use јер, зато што or пошто.
• Откад vs. Кад: Кад / када marks a point in time or simultaneous moment ('when'), whereas откад specifies duration starting from an initiating point ('since / ever since').
• Откад vs. Од тада: Do not confuse their syntactic roles. Откад introduces a dependent clause (or asks 'since when?'); од тада modifies an independent predicate ('since then') and cannot act as a subordinator.