What is the significance of the different declensions and conjugations?

Question

I've been slowly trying to teach myself Latin with the help of this site.

I've gone past the parts where it talks about first, second, third etc declension nouns, and it all seems quite arbitrary as to whether a given noun will be first declension or second declension or etc. In essence, my question is what is it about a first declension noun that makes it a first declension noun rather than a second or third or etc?

Example of the sort of insights which I'm looking for (which may or may not be true):

• "First declension nouns are all masculine whereas second declension nouns are all feminine and third declension nouns are all neuter"

or

• "First declension nouns are all plural, whereas second declensions nouns are all singular and third declension nouns have no number"

I'm also asking this question with regards to the verb conjugations.

What is the pattern? Why is a first declension noun a first declension noun? What is it about a first conjugation verb that makes it first conjugation rather than second conjugation?

What does it actually tell me if I know the conjugation of a verb or the declension of a noun? What information do I get? What do I actually learn about the word?

Or is it actually just arbitrary?

Answer 1

It's pretty much arbitrary.

There are some standard patterns: first-declension nouns tend to be feminine, second-declension masculine/neuter, third-declension abstract concepts, fourth-declension collectives and states, fifth-declension feminine. But there's an exception to each and every one of these rules.

Historically speaking, the declensions derived from different types of Proto-Indo-European nouns. Nouns with stems ending in a became the first declension, o the second, i or a consonant the third, u the fourth, and e the fifth. Hence these vowels appearing in the declension tables.

And there was no real pattern to this, unfortunately. Just like how there's no shared meaning between words starting with the letter M.

Over time, more patterns developed as the language was regularized. This helped somewhat and created the general rules I mentioned above. But in the process irregular nouns like dies were forced into the existing categories, breaking these patterns, and commonly-used nouns stubbornly clung to their existing forms. So you still see words like paterfamilias, from an old first-declension genitive ending -as that died out everywhere else.

The same is generally true of verb conjugations. But this time there was no categorization at all in PIE: in some cases, each principal part was actually a different verb entirely (compare ferō, ferre, tulī, latus).

Latin regularized the verbs far more than other languages did: in Ancient Greek most verbs can't be fit into any "conjugation" at all, and just have to be learned through their principal parts. The common endings like -ō, -āre, -āvī, -ātus developed as the system was simplified and made more regular.

In general, a word's declension or conjugation tells you nothing except how to inflect it properly. Which is quite important, and even has effects in English: cactus → cacti pluralizes like a second-declension Latin noun. But there's no deeper meaning to be revealed by comparing the meanings of words within a particular category: they're just as arbitrary as the Latin genders are.

Answer 2

I don't know if this is specifically the answer you are looking for, but I can explain the different case endings for nouns and verb forms.

Let's start off with nouns.
Nouns in the first declension are typically feminine, with the exception of the Latin words for poet (poeta, poetae) and farmer (agricola, agricolae). I do believe that there is one other, but it is slipping my mind at the present moment. Here is a chart of endings for the first declension.

     |  Singular  |   Plural  |
-----|------------|-----------|
 Nom |     -a     |    -ae    |
 Gen |     -ae    |   -ārum   |
 Dat |     -ae    |    -īs    |
 Acc |     -am    |    -ās    |
 Abl |     -ā     |    -īs    |

Nouns in the second declension are masculine and neuter. The case endings are slightly different between the two declensions, so I have noted the neuter variations in parentheses.

     |  Singular  |   Plural  |
-----|------------|-----------|
 Nom | -us (-um)  |   -ī (-a) |
 Gen |    -ī      |   -ōrum   |
 Dat |    -ō      |    -īs    |
 Acc |    -um     |  -ōs (-a) |
 Abl |    -ō      |    -īs    |

Nouns in the third declension can be masculine, feminine, common (can be either masculine or feminine), or neuter. Again, the neuter variations are in parentheses.

     |  Singular  |   Plural  |
-----|------------|-----------|
 Nom |  (varies)  |  -ēs (-a) |
 Gen |     -is    |    -um    |
 Dat |     -ī     |   -ībus   |
 Acc |     -em (1)|  -ēs (-a) |
 Abl |     -e     |   -ībus   |

¹ Matches nominative

There is also a 4th declension which contains mostly masculine nouns, and a 5th declension which is all feminine save for the word for "day" which is diēs. I can explain these if you would like, but they are generally less common than the aforementioned three declensions.
You may also be wondering about the cases. I'll give a brief explanation below, as I do not know how much you have investigated about this particular area. Keep in mind that this does not cover all the particular uses for each case, but it should give you a relatively useful foundation.
Nominative (nom): the subject of the sentence (ex: the cat chases the mouse)
Genitive (gen): typically indicates possession (the thief took the queen's crown)
Dative (dat): used for reference and as an indirect object with the words "to" or "for" (ex: she gives to the charity)
Accusative (acc): the direct object of the sentence (ex: the cat chases the mouse)
Ablative (abl): used in various prepositional phrases (ex: the cavalry on the bridge was marching with the king.)

Now for verbs!
There are 4 conjugations of verbs, creatively named first, second, third (of which third-io is a sub-conjugation), and fourth.
You can see examples of the different conjugations in one of my previous answers, as I don't want to make this answer too lengthy.
However, I did not include examples of 3rd-io verbs in that answer, so here are a couple:

capio, capere, cepi, captum = seize, capture
facio, facere, feci, factum = do

To answer your last few questions from a general standpoint, noun declensions and verb conjugations allow you to make all the different forms for words so that they can be used in various purposes.
I hope this explanation helps, let me know if you would like any clarification or additional information!