In IELTS Reading completion questions, getting the right word but the wrong grammatical form can cost you the mark. Understanding word forms is a small detail that makes a real difference to your score.
What is a word form? Many English words share a root but change form depending on their grammatical role: "decide" (verb), "decision" (noun), "decisive" (adjective), "decisively" (adverb). Using the wrong form in a sentence, even with the correct root word, often makes the sentence grammatically incorrect.
Why this matters for completion questions. If a blank requires a noun and you write the verb form instead, the sentence will not read correctly, and the answer is likely to be marked wrong — even though you clearly identified the right concept from the passage.
How to check which form is needed. Look at the words immediately surrounding the blank. Is there an article like "a" or "the" before it? That signals a noun is needed. Is there a helping verb nearby, like "is" or "was"? That may signal an adjective or a different verb form. Reading the full sentence, not just the blank, tells you what grammatical role the missing word plays.
Always copy from the passage exactly. The safest approach is to copy the word exactly as it appears in the passage, in its original form, rather than trying to change it yourself. If the passage uses "researchers," write "researchers," not your own guess at "research" or "researcher."
Practice spotting word forms. When reviewing passages, notice the different forms of key vocabulary as they appear across a passage. Readlify's practice passages include a range of completion-style questions where paying attention to word form directly affects your accuracy.