Latin basics: nouns (stems and endings), cases, introduction to declensions

In English a particular noun is spelled the same no matter how it's used.  A tree is a tree is a tree is a tree.  Bob is always Bob unless you want to come up with another name for him, Robert or Bobby or Naughty-pants.  The point is that nouns are spelled the same no matter how they're used.

• Subject:  The church is down the road.
• Indirect Object:  Sally gave the church much of her spare time.
• Object of a preposition:  Joe went into the church to get out of the rain.
• Direct Object:  God blessed the church.
• Predicate Nominative:  That building is a church.
• Possessive:  Joe is a member of the church.

The word is spelled the same no matter how it's used.

In Latin, nouns (and adjectives) have two parts, a stem (at the beginning of the word) and a case ending (at the, duh, end of the word).  The stem stays the same, but the case ending changes depending on how the word is being used, i.e. what part of the sentence it is functioning as.  These different ways that a noun (or adjective can be used are called cases. There are five main cases (and two special ones which I'm going to ignore for now):  Nominative, Genitive, Dative, Accusative and Ablative.

For any noun (or adjective) the five cases can perform the following function:

• Nominative:  Subject, Predicate Nominative, Predicate Adjective
• Genitive: Possessive (ex. "Bob's") and implies "of"
• Dative: Indirect Object and implies either "to" or "for"
• Accusative:  Direct Object or the object of some prepositions
• Ablative: the object of some prepositions or implies "by, with, from"

The stem stays the same for each word (with some exceptions) and it is the case ending that is different and determines what case it is and therefore what part of the sentence it can be functioning as.  Declensions are groups of words that all use the same set of case endings.  Once you learn all the endings, you'll know all the cases of the words of that declension.  There are five declensions, or groups of words, that each use the same set of case endings.

Here's an example.  The nominative case for the word "water" is aqua.  Its stem is aqu-.  Its case ending is -a.  The other case endings are -ae (aquae), -ae (aquae), -am (aquam), -a (aqua).  Technically that last one has a macron (long straight bar) above it and that has to do more with pronunciation than anything else and since I don't want to spend the time figuring out how to type the a-with-a-macron, I'm just going to ignore it for now.  Those five "words" are really all the same word, "water," spelled differently, depending on how it's going to be used in a sentence.

• The aqua is cold.  (Nominative)
• The temperature of the aquae is too chilly for me. (Genitive)
• I was getting a glass for the aquae.  (Dative)
• Bill gave the dog some aquam to drink.  (Accusative)
• Sam climbed from the aqua after a long cold swim.  (Ablative)

These are all for singular cases, i.e. one water, the water, a water.  There is another set of endings (-ae, -arum, -is, -as, -is) for plural cases, waters, the waters, those waters.

Generally, we are taught the cases in this order, the 5 singular cases (-a, -ae, -ae, -am, -a) followed by the 5 plural cases (-ae, -arum, -is, -as, -is) and if you can remember those 10 endings, you've got everything you need for every noun in that declension.

It's a good thing we reviewed the parts of speech and parts of a sentence.  Without understanding those, cases and declensions seem like just arbitrary punishment.  They're not and we'll keep building on these concepts.