Nouns and verbs are great, but sooner or later you'll want to start describing them; sure, you've got a fruit, but what colour is it? What shape is it? Is it hard or soft? How bouncy is it? To answer questions like these you'll probably want some adjectives.
Everyone learns in school that adjectives are words that describe a noun. Because of their close relationship with nouns, many languages will force their adjectives to "agree" with the noun they're modifying. Most of the time this means that adjectives will have different forms depending on the form of their noun. Adjectives can agree with any of the details that we discussed back in nominal morphology: Case, Number, Gender, or anything else that a language might decide to mark on its nouns.
In English, we have nothing like this, so just to make it a little easier to understand here's an example of how English verbs and nouns inflect to match each other.
*The horses eats an apple.
To any English speaker, that sounds incorrect. The problem is that "horses" is a plural word, and "eats" is the third person singular verb "to eat". To make this correct you would have to change the noun to its singular form:
The horse eats an apple.
The other possibility would be to change "eats" to a plural:
The horses eat an apple.
Now that's slightly awkward because it means a bunch of horses are eating one apple, but it's grammatically correct. In many languages, adjectives have to match nouns in the same way that English verbs have to match their subjects. Let's pretend that English had adjectival inflection for a moment. What would it look like?
Singular noun phrases (remember "noun phrases" from earlier?) could look just as they do in real-world English: "solid table", "happy child", "brown dog", "tall woman". Suppose that plural noun phrases had the plural ending "-s" on adjectives: "solids tables", "happys children", "browns dogs", "talls women" — these would all be correct in this hypothetical version of English. The adjectives would become "plural" along with the nouns they modified.
Don't get the impression that the affix that is added to the adjective has to look the same as the one that is added to the noun. I could have said that our hypothetical English has plural adjectives ending with "-pa"; "solidpa tables", "happypa children", &c. It's just that "-s" is a very natural sounding suffix in English.
Returning to reality, languages that have agreement on their adjectives include Greek, Latin, Polish, and Russian. Esperanto is an example of a conlang which does this too: alta viro (a tall man), altaj viroj (tall men). Some languages, such as German, have a complex system of adjectival endings which depend on the gender, number and case of the noun, as well as what type of determiner, if any, precedes the adjective. (Determiners are words like 'a', 'the', 'this', 'all', 'my' etc.)
ein großer Mann "a tall man" der große Mann "the tall man" eine große Frau "a tall woman" die große Frau "the tall woman" ein großes Haus "a big house" das große Haus "the big house" Ich sehe einen großen Mann "I see a tall man."
Remember, any concept that can be marked on the noun can also be agreed with by the adjective, so be inventive. In your own language you may choose to have a similarly complex system, a simple system, or no adjective inflections at all.
The most common kind of inflection that is found only on adjectives, rather than applied to adjectives in agreement with nouns, is comparison. In English, we have three different "degrees" of comparison; positive, comparative, and superlative.
Comparison is a way that two nouns that both possess a certain quality (specified by an adjective) can be compared. Many Indo-European languages have this three-degree system; in some languages, as in English, some words are inflected, some have distinct words for the different forms (suppletion) while others have their comparative forms marked with separate particles. Here's a table of some of the English forms:
There are other possibilities, as well. A system of augmentative or diminutive affixes might be used for both nouns and adjectives, and take the place of comparative forms; so the same affix might turn "hill" into "mountain" and "strong" into "stronger" or "very strong". There might be only two, or more than three degrees of comparison in the system.
Most people think of adverbs as being just like adjectives except that they help to describe verbs instead of nouns. But actually, adverbs can be used to describe more than just verbs:
- "She ran quickly."
- "The ball is definitely red."
- "Naturally, he did what he could."
This apparent versatility comes from the fact that adverbs are a "catch-all" category. That is, when people find a word that isn't a noun, verb, or other known part of speech they'll usually call it an adverb regardless of whether it can be used to describe verbs.
Distinction of verbs, adjectives, and adverbs edit
In English, French, Greek and many other Indo-European languages it makes sense to describe verbs, adjectives, and adverbs as three different "parts of speech". But in some languages, like German or Turkish, adjectives and adverbs are essentially the same part of speech; the same word in the same form can modify a noun or a verb, if it makes sense to do so. For example, in English we use an adjective like "fast" to describe nouns and an adverb like "swiftly" to describe verbs, but German uses the word "schnell" for both.
In some other languages, there is no distinct category of adjectives as opposed to verbs; the meanings expressed by adjectives in English, Greek and so forth are expressed by stative intransitive verbs. Esperanto allows modifier root words to be inflected as adjectives, adverbs or stative verbs as the speaker thinks suitable:
Li kuras rapide "He runs quickly" (adverb) Li estas rapida "He is quick" (adjective) Li rapidas "He quicks (hurries)" (stative verb)