Morphology is the study of morphemes, obviously.  Morphemes are words, word stems, and affixes, basically the unit of language one up from phonemes. Although they are often understood as units of meaning, they are usually considered a part of a language's syntax or grammar.  It is specifically grammatical morphemes that this chapter will focus on.

It is in their morphology that we most clearly see the differences between languages that are isolating (such as Chinese, Indonesian, Krewol...), ones that are agglutinating (such as Turkish, Finnish, Tamil...), and ones that are inflexional (such as Russian, Latin, Arabic...).  Isolating languages use grammatical morphemes that are separate words.  Agglutinating languages use grammatical morphemes in the form of attached syllables called affixes.  Inflexional languages may go one step further and actually change the word at the phonemic level to express grammatical morphemes.

All languages are really mixed systems -- it's all a matter of proportions.  English, for example, uses all three methods:  To make the future tense of a verb, we use the particle will (I will see you); to make the past tense, we usually use the affix -ed (I changed it); but in many words, we change the word for the past (I see it becomes I saw it).  Looking at nouns, sometimes we make the plural with a particle (three head of cattle), sometimes with an affix (three cats), and sometimes by changing the word (three men).  But, because we still use a lot of non-syllable affixes (such as -ed, usually pronounced as d or t, and -s, usually pronounced as s or z, dependeing on context), English is still considered an inflexional language by most linguists.

Affixes

Most languages, but especially agglutinating and inflexional ones, differentiate between the stem of the word, which carries the basic meaning, and various affixes or attachments that carry additional, often grammatical, meanings.  There are several kinds of affixes:

 Suffixes are attached to the end of the stem;
 Prefixes are attached to the front of the stem;
 Infixes are put in the middle of the word;
 Ablaut is a change in a vowel that carries extra meaning;
 Reduplication is a matter of doubling a syllable to do the same.

Suffixes are the most common, and English uses them.  For example, the past tense of most verbs is a matter of adding -ed to the stem; the present participle is made by adding -ing; the plural of a noun is made by adding -s.

Turkish is an example of an agglutinating language that makes extensive use of suffixes.  One example I found on the internet (Learning Practical Turkish) is the word terbiyesizliklerindenmis:

Ablaut is common in English and its Germanic cousins.  For example, the past tense of sing is sang, and the past participle is sung.  The plural of goose is geese.  Ablaut seems to come from former suffixes that influenced the pronunciation of the vowel, then disappeared over time.  Goose-geese was once gos-gese, and before that gos-göse, and before that gos-gose.  The plural suffix -e caused the fronting of the vowel o to ö and then e.

Infixes are best illustrated by the Semitic languages, such as Arabic.  Many words in Arabic are composed of three consonants, and many of the grammatical variations are produced by altering the vowels between and around them.  For example, the root for writing is ktb:

Nouns

Nouns are words that name or denote a person, thing, action, or quality.  They are “thing” words -- although “things” can include all sorts of abstract ideas that might otherwise look more like verbs or adjectives.  In various languages, they are marked, by affixes or particles, as to their number, gender, definiteness, and especially cases.

Definiteness concerns the extent to which we are talking about a specific thing or event, one that is known to the speakers, or about something less well defined, such as any old thing, or something not specific.

In English, the definite is marked by the article the.  It can also be marked by other words, such as this, that, my, yours, and so on.  The indefinite is marked by the article a or an, as well as the plural without an article, or words such as one, two, some, any, etc.  On the other hand, many languages don't use articles at all -- Latin, Russian, Hindi, and Chinese come to mind!

In a number of languages, the definite is marked with a suffix.  This is true of Swedish, Danish, Norwegian, Icelandic, Rumanian, Bulgarian, and Albanian, among others.  The Scandinavian languages are, of course, closely related, so we would expect them to share a feature like this.  But Rumanian, Bulgarian, and Albanian are only distantly related. It seems that they influenced each other, or perhaps there were people living in the Balkans in ancient times who influenced them all.

Number, of course, refers to how many of the item we are talking about.  There are three common numbers:  Singular, meaning one; plural, meaning more than one; and somewhat rarer, the dual, meaning two.  You can see the significance of the dual in our own use of words such as couple, pair, and so on.  Again, many languages do not mark the plural, much less the dual.

The most complex aspect of nouns is cases, also known as declensions.  Philosophers in ancient Greece and India were already discussing this as much as 2500 years ago!  Much of the terminology we still use today was invented during the Roman Empire, and reflects the cases used in Latin.

The first case is the nominative, roughly the subject of the sentence.  In many languages, it is the basic form, sometimes represented by the bare stem.  A second case is the vocative, which is the form used when calling out to someone, sort of like “Oh, Claudius!”  The rest of the cases are referred to as oblique or objective.  Languages that make many distinctions among the oblique cases use them in the same way that other languages use prepositions or postpositions.

Accusative -- the direct object of the verb:  He threw the ball.

Dative -- the indirect object:  He threw it to John.

Ablative -- expressed in English with the preposition from: He threw from first base.

Locative -- expressed in English with prepositions such as at or in:  We were at the hotdog stand in the stadium.

Genitive -- the possessive form, often expressed in English with the word of, but also with the case suffix ‘s:  It was John’s ball.

Instrumental -- expressed in English with prepositions like with:  He hit it with a bat.

Sociative -- also expressed in English with with, but now referring to people:  I went out with her.

There are many others.  A language in the Caucasus Mountains called Tassaran has 48 noun cases!  However, many linguists point out that cases should only refer to inflexional languages such as Latin.  Agglutinative languages such as Finnish can be better thought of as having postpositions that are attached to the noun, since they are very consistent and easy to recognize, unlike the cases in Latin.

Here is an example of the Russian word for country, singular and plural:

Compare that with an example of the word for man in Tamil, a Dravidian language of southern India:

Although there are even more cases, these endings are the same for all other nouns! And notice how the plural is just a matter of sticking kal inbetween the stem and the affix?.

Gender is perhaps the oddest noun variation.  It is called gender because it is -- loosely -- tied to the physical sex of people and animals.  Many languages differentiate between masculine nouns and feminine nouns, with different endings for each, and requiring different articles and adjective forms along with them.  French, Spanish, Italian, and Portuguese are examples.

Other languages, such as German, count three genders:  Masculine, feminine, and neuter.  Neuter presumably refers to things that don’t have a gender, but there is little consistency there.  In Dutch, there are two genders, but they are neuter and common, common deriving from what was originally masculine and feminine.  English nouns have no gender.

Many languages outside the European sphere differentiate between animate and inanimate, one referring to people, animals, and spirits, the other to things.  And there are many languages that make many differentiations:  Bantu languages, for example, have many noun categories, such as "long, thin things," "body parts," "places," and so on.

In Chinese, there is a strong isolating (non-affix) version of this:  When you want to indicate more than one of something, you must use a special word called a classifier between the number and the object.  This is analogous to the way we might say three head of cattle.

There are still more examples of noun variation:  Diminutives express smallness (dog becomes doggy, for example), and augmentatives express largeness.  Diminutives are often also used to express affection, and augmentatives sometimes express danger or evil.

Some languages have a variety of honorifics, often suffixes or prefixes that indicate status.  The Japanese -san is a well known example.  There are also affixes that indicate lowly status, and in some languages several different degrees of status!

Pronouns

Pronouns are words that serve as place-holders for nouns.  Instead of referring to a person by his or her name, we use he or she; instead of naming something repeatedly, we refer to it as it.  Pronouns have many of the same variations as nouns, including gender, number, and case.  There are also three persons that are differentiated in most languages:  First refers to the person speaking or his/her group (I, me; we, us); Second person refers to the person spoken to or his/her group (you); And the third person refers to other people outside the conversation or to things (he, him, she, her, it, they, them). In English, for example...

("Oblique" is the name for a case that covers the objects of a verb or any preposition.)

For comparison, here's the Icelandic declension of the pronoun anyone:

In some languages, there are two forms of the third person plural:  One is inclusive, and refers to the speaker and the listener together (Why don’t we go have a drink together sometime?); the other is exclusive, and refers to the speaker’s group distinct from the listener (We are going to beat your team!).

There are also pronouns that reflect the action back onto the subject -- appropriately named reflexive pronouns.  In English, they are often nicely marked with -self (myself, yourself, himself, etc.).  In many languages, there is a generic reflexive for the third person singular or even third person singular and plural.  In Spanish, for example, that function is performed by the single word se.

Politeness is often an issue with pronouns.  In many European languages, there is a distinction made between a familiar and a formal version of the second person singular.  In French, for example, you call your friends tu and your parents, teachers, or boss vous.  You don’t switch to tu until it is subtly agreed between the two of you that it is okay to “tutoyer.”  In some Asian languages, there is considerably more detail involved.

There are other kinds of pronouns besides the personal ones.  Demonstrative pronouns include this, that, these, and those.  Many languages have three sets of these, one for things nearby the speaker, one for things nearby the listener, and one for things away from either.

Indefinite pronouns include words such as someone, anyone, many, and so on.  Like the indefinite article, they don’t indicate precisely whom are what we are talking about.

Interrogative pronouns are used to ask question:  Who is that man?  Relative pronouns are used to connect a noun with a phrase that gives more detail about the noun:  He is the one whom you saw yesterday.  As you can see, in English, they are often the same!

Verbs

Verbs are words which express action taken by something, the state something is in or a change in that state, or an interaction between one thing and another.  Like nouns, there are many variations of verbs.

Transitive verbs are ones that have both a subject and an object: John hit the ball.  John is the subject and ball the object of the verb hit.  Intransitive verbs are ones that only have a subject: I laughed.  There is nothing that is laughed (except, I suppose, the laugh itself.)  Many verbs have an intermediate form called the reflexive, meaning that the subject is also the object:  I hurt myself.  As the example shows, reflexive verb forms often take a reflexive pronoun as their object!  But there are reflexive verbs that don’t: They got married.

The biggest issue with verb forms is conjugation.  In some languages, it is a fairly simple matter; in others, there are a huge variety of affixes.

Most familiar to Europeans are tenses.  Many languages differentiate between the past tense, the present tense, and the future tense.  Some languages also differentiate various details of timing, such as an immediate form, a proximate form (near in time), and a distal form (the distant past or future.)  Quite a few languages (Russian and Japanese included) only distingish past from "non-past."

In French, I sing goes through the following changes:

There is a passive version of the perfect called the effective.  In English, an example might be He got seen.

The imperfect (aka durative or continuative) has an ongoing tone to it:  The action continues through the moment.  In English, we use a form of the verb to be followed by the present participle:  I was saying, I am saying, I will be saying.

There are a number of variations on the imperfect aspect.  The progressive -- I have been saying -- suggests that the action started a bit earlier and continues through the present.  The iterative (aka repetitive) -- I keep saying -- indicates that a single action is repeatedly performed.  And the inceptive (aka commencement) -- Let’s get going -- says to us that the action should get started.

Finally, there is the simple (or indefinite) aspect.  This includes the usual tenses used as is:  I said, I say, I will say.  The simple past is often called the preterite.

Next up is mood or mode.  The basic form is the indicative:  We are saying something that happened, is happening, or will happen.  A version of the indicative is the stative, which indicates that someone or something is in a particular state, as opposed to taking a particular action:  He sits.

The next three are used when there is a degree of unreality involved, and are often blended together.  The optative (aka desiderative) indicates a desire or wish for something to happen.  In English, this is usually expressed with auxiliary (helper) verbs such as should or would, as well as with expressions such as I wish....

The conditional mood is used when the reality of one event depends on the reality of another:  I will go if you go.  English has the remnants of a conditional:  We say If I were to go... rather than If I was to go....  But it is rapidly going the way of the who-whom distinction!

The subjunctive mood is used when there is some doubt or uncertainty about the event.  Many languages have entire conjugations of subjunctive, in various tenses and aspects.  It was the bane of my high school French class.

There are other moods.  In Japanese, for example, there are provisional and tentative versions of verbs.  And many languages have the imperative: Do this!  In English this is expressed by leaving out the subject (you).

In French, the aspect and mood variations on I sing look like this:

Next, we have various voices.  The active voice is the basic one.  It is used when the subject performs an action.

The passive voice is used when the subject of the sentence is actually the object of the action.  In English, we use a form of to be with the past participle:  I was hit.

The causative is a voice used when the subject causes the object to perform an action, as in He made me do it.

When the causative is combined with the reflexive, it is called the dynamic: They married themselves!

Person is an aspect of verb forms in many languages.  Most commonly, there is an ending or other affix that indicates something about the subject (such as first, second, or third person, gender, and singular or plural).  In English, the only person ending left in almost all verbs is the -s in the third person singular of the present tense (he does, vs I, you, we, he, she, it, or they do).

There are languages (Basque comes to mind) where the direct object and even the indirect object is also included in the verb form.  Dakarzkizu, for example, means he brings them to you, while Zenekarzkidan means you brought them to me. (Kar is the piece of these words that is the equivalent to bring in English)

Here's a simple French conjugation, in the present tense, showing person:

Another common verb variation is the negative.  In English, we use the word not after one of several auxiliary (see below) verbs.  There is a tendency, however, for many verbs to change in the negative, by combining with the not:  I can’t, I won’t, I don’t, I ain’t....  Although we can still see where they come from (and the apostrophe reminds us),  they are well on there way to becoming separate forms.

There are other languages where the verb changes when it is a part of a question.  In Irish, for example tá (to be) becomes an bhfuil in questions.

I can't move on without mentioning that in Hausa (a language of Nigeria), tense, aspect, etc., are indicated with variations of the subject pronoun, not the verb, as in these example of the word for he:

(It might surprise you to know that we are moving this way in English, too:  I'd, I've, I'll, etc.)

In isolating languages such as Chinese, or in languages moving strongly in that direction, such as English and French, many of the preceding variations are not done by adding endings or changing the verb.  They are done with auxiliary verbs.  In English, for example, we say He will sing, rather than Il chantera as in French.  In French, on the other hand, we often say Il a chanté instead of He sang.  These particular examples are called compound tenses, but they can also involve aspects and moods and so on.

Participles are forms of the verb that are often used in such compound verbs.  In English, we have two:  The past participle (which usually ends in -ed, just like the past tense) and the present participle (which ends in -ing).  Participles are also used as adjectives: He is a dancing fool.  He was a beaten man.  And they can even be used as nouns:  Help the down-trodden.  Winning is everything.  Note that the past participle is often referred to as the passive participle, and the present participle as the active participle.

Another form of the verb often used in compound verbs is the infinitive.  In English, we don't have a real infinitive form -- we just put to in front of it:  To sleep, perchance to dream....  And so we say He wants to run, a compound made with wants plus the infinitive of run.  In many languages, there is a special form.  In French, for example, it usually ends in -r, and is used as the dictionary form.

There are many forms of verbal nouns (gerunds) -- i.e. verbs used as nouns, with or without special endings.  The infinitive and the participles are examples.  But we can also use the verb as is in many languages -- English being the best example, since we do it all the time:  I dance and I go to the dance and I do a dance!

Other Parts of Speech

Adjectives are words which modify nouns.  In many languages, adjectives have affixes that must agree with their nouns in case, number, gender, etc.

One peculiar feature of adjectives in many language is comparison:  There may be special forms of the adjective when you are using it to say that a noun is more or less of whatever quality the adjective expresses (the comparative form), or that is is the most or least of that quality (the superlative form).  In English, we still see special words like good/better/best, regular endings such as big/bigger/biggest, and analytic forms such as significant/more significant/most significant.

Adverbs are words or phrases which modify verbs, adjectives, or even other adverbs.  There are often special endings that differentiate adverbs from similar adjectives:  In English, adverbs often end in -ly; In French, they often end in -ment.

Numerals (or just numbers) often come in both adjective and adverbial forms.  In Shakespeare's time, we said three men, but it was done thrice.  Today, of course, the latter is analytic: It was done three times.

The simple form of numerals is the cardinal number, which indicates a certain quantity of something.  There is also the ordinal number, which indicates the position of something in a sequence: He was the third man.  We see a analytic construction more and more frequently today:  He was her number one man, or she was bachelorette number three.

Prepositions are words which can allow a noun to qualify another noun or a verb in a way that parallels adjectives or adverbs:  The man in the yard ran into the house.  Many languages -- Japanese, for example -- have postpositions instead of prepositions, but they serve the same purpose.  Noun cases are often a substitute for prepositions or postpositions, and may in fact have developed out of them.

Irish is interesting in that its prepositions ofen vary by person, just like verbs:  Here is the "conjugation" of the preposition roimh (before) (mh is pronounced w):

Finally, there are interjections.  Interjections are expressions of emotion -- not true words but rather vocal noises that reflect the feelings of the speaker:  Oh!  Huh?  Hey!  Shit!  The last one is, of course, also a regular word, but its use in this case has nothing to do with what it literally refers to.