Evidence-based answer · Last updated · How it’s made
Across studies of adult learners writing in Turkish, spelling/orthography and morphological (word-ending) errors are consistently the most common problem, outranking sentence-structure (syntax) and vocabulary errors. Within morphology, case suffixes (like the accusative "-i" or locative "-de"), possessive endings, vowel harmony, and gerund/participle endings used to link clauses are the specific trouble spots, with error rates rising as the target structures get more complex or less similar to the learner's first language.
Answered for language learning in general. No specific language was set for this question, so the findings are drawn from general second-language research rather than one language’s literature.
A systematic review of 16 studies on written Turkish produced by foreign adult learners found spelling/punctuation errors were most frequent (40%), followed by grammatical errors (34%), then vocabulary errors (14%) and sentence-structure errors (12%).2
In a comparison of Turkish learners studying inside versus outside Turkey, spelling errors were most frequent overall, but among grammar-related errors, mistakes in word endings (morphological errors, about 32-53% of grammar errors depending on group) clearly outnumbered sentence-structure/word-order errors (about 12-16%).3
In plain terms
Within word-ending errors, learners most often mis-produce case suffixes (which mark grammatical roles like object or location), person markers, and possessive markers, a pattern reported consistently across several studies of Turkish learners' writing.3
When sentence-structure errors do occur, the single most frequent type is incorrect word order in simple sentences, found in both learners studying in Turkey and those studying abroad.3
A detailed error-frequency analysis of learner writing found that, after letter/spelling errors, the most common grammar-related error categories were problems forming noun phrases, adding unnecessary extra suffixes, misusing the accusative case suffix ('-i'), misusing possessive suffixes, misusing the locative case suffix ('-de'), vowel harmony mistakes, and misusing the dative case suffix ('-e').5
In plain terms
Among Arab learners of Turkish at an advanced (C1) level, gerunds and gerund-like connector suffixes that join clauses together (used to express ideas like 'in order to,' 'while,' or 'when') were used frequently, but certain less-common ones — such as '-(y)IncA' ('as soon as/when'), '-mAsI için' ('in order to'), '-DIğI zaman' ('when'), and '-mAdAn önce' ('before') — had notably higher error rates than the most-practiced ones.1
In plain terms
Researchers attribute many of these frequent morphological and connector-suffix errors to structural differences between Turkish and learners' native languages, such as Arabic's different sentence structure, clause-linking patterns, and its gender/number agreement system, which Turkish gerund suffixes do not need to track in the same way.1
A separate study found that learners of Turkish continue to make errors with verb valency — that is, which case-marked nouns a given verb requires (for example whether a verb needs its object in the dative or accusative form) — even as their overall proficiency improves, and this error type does not resolve on its own without targeted teaching.4
In plain terms
Given that spelling and word-ending (morphological) accuracy — not sentence structure — are the biggest stumbling blocks in written Turkish, learners should prioritize targeted practice on case suffixes (accusative, dative, locative), possessive and person markers, and vowel harmony rules, ideally through dictation and writing practice that gets corrected suffix-by-suffix rather than only at the whole-sentence level. Learners whose first language differs structurally from Turkish (such as Arabic speakers) should pay particular attention to the less-common gerund and clause-connector suffixes (like '-(y)IncA', '-mAsI için', '-DIğI zaman', '-mAdAn önce'), since these show disproportionately higher error rates even at advanced levels; explicit grammar lessons and focused sentence mining of these specific patterns from real texts may help. Because verb valency (which suffix a given verb requires on its object) does not seem to self-correct with general exposure, structured lessons or tutoring that specifically drill verb-suffix pairings appear useful.
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