What are word forms, and how do you choose the correct noun, verb, adjective or adverb in a sentence?

In one line

Word forms are the different grammatical versions of the same word (noun, verb, adjective, adverb), and the sentence position decides which form is correct.

Explained simply

'Decide', 'decision', 'decisive' and 'decisively' are one family. It's like the same person in different uniforms: you pick the uniform that fits the job in the sentence.

Technically, word formation uses suffixes to move a base across parts of speech. Exam items give a sentence with a blank and a base word; you must pick the form that fits grammatically. This is a standard verbal-aptitude item in tests like TOEFL, IELTS, CAT and GRE.

How it works

1. Look at the blank's neighbours:
2. After an article (a, an, the) or a possessive (his, our), or as a subject/object, use a noun: 'The decision was final.'
3. After a subject or a modal/auxiliary (will, can, should), use a verb: 'We must decide today.'
4. Before a noun, or after 'be/seem/become', use an adjective: 'a decisive leader'; 'She was decisive.'
5. Describing a verb, adjective or the whole sentence, use an adverb: 'She acted decisively.'

6. Noun	Verb	Adjective	Adverb
   analysis	analyse	analytical	analytically
   efficiency	(none common)	efficient	efficiently
   strength	strengthen	strong	strongly
   success	succeed	successful	successfully
   simplicity	simplify	simple	simply

Quick example

Fill in with the correct form of 'success': (a) Her ____ surprised everyone. → success (noun, after 'her'). (b) She hopes to ____ in the exam. → succeed (verb, after 'to'). (c) It was a ____ launch. → successful (adjective, before noun). (d) The rocket landed ____. → successfully (adverb, describing 'landed').

Common mistakes

• Using an adjective where an adverb is needed: 'He speaks fluent' instead of 'He speaks fluently'.
• Confusing 'analysis' (noun) with 'analyse' (verb): 'We will analysis the data' is wrong.
• Writing 'succeed' as a noun ('Her succeed').

How MU asks it

Asked as fill-in-the-blank or MCQ items ('Use the correct form of the word given in brackets'), usually 1 mark each in sets. For full marks: identify the slot (noun, verb, adjective, adverb) from neighbouring words, then choose the form, and check spelling.