Understanding the Third Conjugation

Here are two important rules for you to remember:

(1) the thematic vowel in third conjugation is a short vowel; it appears as -i- or -u- in the present and -e- in the imperfect
(2) The tense sign for the future in third conjugation is -e-; the future tense in third conjugation uses no thematic vowel

Third conjugation has the most number of irregularities of the four conjugations in Latin. Here is an example of a third-conjugation verb, scribo, which means “write,” conjugated in the present tense:

Scribo  Scribimus

Scribis  Scribitis

Scribit  Scribunt

Notice that the formation of the present tense in third conjugation follows a pattern similar to that seen in first and second conjugation.

Take a third-conjugation verb base
add a thematic vowel (Which will be fairly irregular in this conjugation)
and to that, append personal endings.

Note: the personal endings are the same as those in first and second conjugation. But unlike the -a- which dominates first conjugation or the strong -e- which dominates second, third uses a short vowel which readily changes form as it encounters different consonants. Here are somethings to consider and think about:

So, like we see, it will appear as -i- in the second person and third person singular and the first and second person plural.
In the third person plural it appears as -u- and in the first person singular there is no thematic vowel, the same way the -a- in first conjugation disappears in forms like laudo or amo.
The translation of third-conjugation verbs differs in no way from verbs in first and second conjugation. So there’s no point in rehearsing what you already know. Scribo, for instance, would translate as “I write,” “I am writing,” “I do write;” the other persons and numbers would follow suite within the same paradigm.

Imperfect

As for the imperfect tense in third conjugation poses even fewer problems than the present. Just like in first and second conjugation, it uses -ba- as the marker for the imperfect. Thus the imperfect of scribo goes: scribebam, scribebas, etc.
Note that unlike in the present the thematic vowel in the imperfect is -e-. The imperfect tense in third conjugation translates the same way it does in first and second; it denotes an incomplete or repeated action in the past. And therefore scribebam translates as “I was writing,” “I used to write,” “I kept on writing.”

Future

Unlike the -bo, -bis, -bit business you are used to from first and second conjugation, third conjugation uses -e- as its future tense marker. This -e- which is easily confused with the second conjugation thematic vowel will present manifold challenges and only goes to demonstrate how important it is to distinguish between second- and third-conjugation verbs.
To make matters only worse, the -e- isn’t used universally. In the first person singular, the future tense marker is -a- rendering a conjugation that looks like:

scribam “I will write,”

scribes “you will write,”

scribet “he will write,” and so on...

And even worse yet, note that this tense marker eats up the thematic vowel. So there’s no thematic vowel at all in third-conjugation future.