FINITE AND NON-FINITE VERBS (UNINFLECTED VERBS)

Finite and non-finite verbs

Finite verb forms show tense, person and number (I go, she goes, we went, etc.):

She was waiting in the room before he came in.

Does your brother know my brother?

The night before he had to leave, they sat on the small sofa in the living-room and looked at old family photos.

Aren’t you a bit late?

Non-finite verb forms (verbals) do not show tense, person or number. Typically they are infinitive forms with and without to (e.g. to go, go), -ing forms and -ed forms (e.g. going, gone):

She tiptoed round the house so as not to wake anyone.

You need to paint the whole cupboard, starting from the bottom.

[from a biography]

Taken prisoner by the British in December 1776, he was held in New York City for a year …

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What Are Non-Finite Verbs?

A non-finite verb (also known as a verbal) is the term used to describe a verb that is not showing tense.

In other words, it a verb form which is not acting like a verb (or, at least, the type of verb you need to form a sentence).

There are three types of non-finite verbs: gerunds, infinitives, and participles. Look at these examples (non-finite verbs shaded):

• I hate camping.
(Camping is a non-finite verb. In fact, it is a gerund, i.e., a noun formed from a verb. The giveaway for a gerund is the -ing ending.)
• I want to go there.
(To go is a non-finite verb. It is an infinitive, i.e., the base form of a verb. The giveaway for an infinitive is often, but not always, the to before it.)
• We ate our roasted marshmallows.
(Roasted is a non-finite verb. It is a participle, a type of adjective. There is no real giveaway for a participle, but lots of participles end in -ed and -ing.)

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Inflection

In grammar, inflection or inflexion – sometimes called accidence – is the modification of a word to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, and mood. The inflection of verbs is also called conjugation, and one can refer to the inflection of nouns, adjectives, adverbs, pronouns, determiners, participles, prepositions, postpositions, numerals, articles etc, as declension.
An inflection expresses one or more grammatical categories with a prefix, suffix or infix, or another internal modification such as a vowel change.

Uninflected word

In linguistic morphology, an uninflected word is a word that has no morphological markers (inflection) such as affixes, ablaut, consonant gradation, etc., indicating declension or conjugation. If a word has an uninflected form, this is usually the form used as the lemma for the word.^[1]
In English and many other languages, uninflected words include prepositions, interjections, and conjunctions, often called invariable words. These cannot be inflected under any circumstances (unless they are used as different parts of speech, as in "ifs and buts").
Only words that cannot be inflected at all are called "invariable". In the strict sense of the term "uninflected", only invariable words are uninflected, but in broader linguistic usage, these terms are extended to be inflectable words that appear in their basic form. For example, English nouns are said to be uninflected in the singular, while they show inflection in the plural (represented by the affix -s/-es).
https://en.wikipedia.org/wiki/Inflection

Examples in English

In English most nouns are inflected for number with the inflectional plural affix -s (as in "dog" → "dog-s"), and most English verbs are inflected for tense with the inflectional past tense affix -ed (as in "call" → "call-ed"). English also inflects verbs by affixation to mark the third person singular in the present tense (with -s), and the present participle (with -ing). English short adjectives are inflected to mark comparative and superlative forms (with -er and -est respectively).
There are 9 inflectional affixes in the English language.

Inflectional Affixes in English

Affix	Grammatical Category	Mark	Part of Speech
-s	Number	plural	nouns
-'s/'/s	Case	genitive	nouns and noun phrases, pronouns (marks independent genitive)
-self	Case	reflexive	pronoun
-ing	Aspect	progressive	verbs
-en/-ed	Aspect	perfect non-progressive	verbs
-ed	Tense	past (simple)	verbs
-s	Person, Number, Aspect, Tense	3rd person singular present	verbs
-er	Degree of Comparison	comparative	adjectives (monosyllabic or ending in -y or -ie)
-est	Degree of Comparison	superlative	adjectives