So we just covered a large chunk of grammar, but we've mostly kept to nouns and there's a whole lot more to cover besides that, part of which we'll cover in this third part.
We'll first cover adjectives. Adjectives may seem like a fairly static part of a sentence, but there are many variations on how you can express an adjective and on how they change depending on other elements in a sentence.
After that we'll cover verbs and how they may or may not change depending on a whole range of possible elements, like time, urgency and completion of an action.
After this part we'll cover the smaller parts of grammar, things like numbers and pronouns.
Adjectives are very flexible in terms of how you use them in your language. They can be like nouns, they can be like verbs and they can be their own unique element with their own rules, which is what they are in English.
If adverbs are their own word class they won't have to follow the same rules nouns and verbs may have to follow, like indicating gender or politeness. It's an easy and straight forward system. 'The big, red car is nice'. 'Big' and 'red' remain unchanged, the only rule they follow is their position in the sentence, which could be anywhere you want in your language, but in English they come before the noun they modify.
When an adjective is like a noun things will become trickier. Nouns can have a gender, a plural form and a lot more, this means the adjective will have to reflect the same. Let's add gender to English nouns to illustrate this point. We'll use 'in' for female and 'on' for male.
The sentence 'the short, blond (female) kid is nice' would become 'the shortin, blondin, kidin is nice'. If the sentence is 'the tall, young man is nice' it would become 'the tallon, youngon manon is nice'. Although man could remain man as it already indicates gender on its own.
It may seem like an odd system if you're not used to it, but there are many languages which use adjectives as nouns, including Latin, Spanish, Celtic and German, though not all to the same degree.
Adjectives can also be used as verbs. Japanese does this with 'i adjectives', which are adjectives which usually end in a hiragana i, but that's besides the point. The point is that when adjectives are used as verb they conjugate like verbs.
In Japanese this goes as follows: 'It is cold' would be 'samui desu', in which 'samui' means cold. 'It was cold' turns into 'samu katta desu'. 'It was not cold' becomes 'samu kuna katta desu'.
As mentioned in the previous part you can also get rid of adjectives by turning them into nouns or verbs.
Adjectives usually have a comparative and superlative form. 'Sweeter' is the comparative form of 'sweet' and 'sweetest' is the superlative form. In English you'd usually express the comparative form by adding 'er' and 'est' for the superlative, as in 'cool - cooler - coolest', but there are plenty of irregular adjectives to break this rule, like 'good - better - best' and 'many - more - most' and some adjectives can only be compared by using 'more' and 'most', like 'beautiful - more beautiful - most beautiful'.
Not all languages have 3 steps, some simply have the base adjective and the 'more' version. Others might have more steps to indicate further steps, like slightly more and almost the most. How many you want will be up to you, but determining how many would best suit your language could be done by looking at the culture behind your language. Does it have a need for 'almost the best' or 'slightly better'?
Many languages have adverbs, which are essentially adjectives which are mostly applied to verbs, adjectives and other adverbs, rather than nouns and pronouns, but some words can work as both an adverb and an adjective.
In the sentence 'the slow man' 'slow' is an adjective, but in the sentence 'The man walks slowly' 'slowly' is an adverb. In English, most adjectives can be turned into an adverb by adding 'ly', your language could use something similar or maybe a prefix instead or maybe nothing at all.
Adverbs answer the question 'how, when, where and to what extend does something do something'. But there are languages which don't use adverbs for this, they simply stick to adjectives and they might let the word order or the context provide that function, but some show no difference at all, with the exception of what comes after the adjective (nouns or verbs or anything else).
An example: the sentence 'the bad written book' is wrong in English, you'd say 'the badly written book', but you can still understand the first sentence and many languages didn't see a need for adverbs, perhaps for that very reason.
Time for another big chunk of rule creation: verbs. Verbs can change a lot, whether it's to reflect a tense, a honorific or even urgency, there's a whole lot of creative freedom here, but also a whole lot to cover. We'll start with a relatively easy one.
In English we only reflect the singular third person in verbs by adding an 's' at the end (I read, you read, he/she/it reads), but some languages reflect every person in the verb, like Spanish, and some languages don't reflect anything at all, like Japanese.
Some languages reflect both the subject and the object, so verbs would indicate who's speaking and who that person or those people are speaking to. 'We speak ill of you' could be written simply as 'speak ill', but speak would be altered to reflect who's speaking and who's being spoken to. For example, let's say if the plural first person (We) is the subject we add 's' to the end and if the singular second person (you) is the object we add 'on', the sentence would become 'speakson ill'.
With this system you can pretty much get rid of personal pronouns (I, you, etc), since the verb already indicates them.
The tense of a verb indicates when the action takes place, which, in English, can be either the past, the present or the future. Some languages only distinguish between past and non-past, so the present and future aren't distinguished from each other.
English doesn't distinguish between present and future by changing the verb either, instead we use 'will' or 'going to' (I will work/I'm going to work').
Not all languages use tenses though, some use adverbs like 'tomorrow', 'yesterday' and 'all day' to indicate time.
In English we have 17 different tenses, each with their own purpose to indicate a specific time frame, but your language doesn't need them all and at the same time it could use more if you wish.
I've created a grammar creator with a list of the 17 English tenses to help you create the rules of conjugating verbs for however many tenses you wish, you can find the tool right here.
There's a whole range of possible tenses and other elements you can use to change verbs, some of which are as follows:
Aspect: Whether the action is an ongoing action and whether an action is a single action or a repeated one, perhaps on a habitual basis.
Completion: Whether the action is completed or not.
Deference: Whether the polite form of a verb is needed or not. Japanese has a lot of different forms of politeness.
Dynamic or static: Whether an action is unchanged or changed in state. For example, a verb in its static form could mean 'sleeping' and its dynamic form could mean 'going to bed'.
Evidentiality: Whether an action is told from first- or secondhand experience or whether it's simply something that probably happened.
Imperative: The commanded form of a verb, which can be expanded to suggestions, demands, requests and so on.
Mood: Whether the action is certain to be performed, simply desired and wanted or not happening at all.
There are many more possible tenses you can create, but which ones you need will probably depend mostly on the culture behind your language and partially on what you like it to have, if you want any at all. For example, a highly militaristic society (especially one at war) will likely put importance on whether an action is firsthand experience or not, as that could reflect on how accurate the information might be.
There are also many different ways to indicate a tense, whether it's by adding a small phoneme, like 'ed' in 'worked' or by adding a free phoneme, like 'will' in 'will work' or by changing the word order or pretty much anything else you can come up with.
The verb 'to be' also serves as a copula in English. A copula is something which links the subject with everything else relating to that subject. For example, in the sentence 'The red car is driving at the suggested speed limit' the word 'is' links 'the red car' with 'driving at the suggested speed limit'.
Not every language has a copula, some have multiple and some have one, but not 'to be' and some use a different copula for specific purposes. For example, in French you use 'to have' when you talk about your age. "J'ai 7 ans" means "I'm 7 years old", but literally translates to "I have 7 years.".
Speaking of 'to have', some languages do not have this verb, instead they'd say something along the lines of 'a dog is with me' instead of 'I have a dog'.
Many more verbs are 'missing' from some languages, which is completely natural. You wouldn't have the verb 'to mine' if there's no such thing as mining in that culture, but we'll delve deeper into this in the final part of this guide when we create the vocabulary of our language, but first we'll need to cover the last bits and piece of grammar, which we do in the next part.