Aorist is the default form to show past tense; its aspect is undefined. Aorist verbs always take an augment.
Aorist verbs are further distinguished into first aorists (BBG chapter 23) and second aorists (BBG chapter 22). This is the same difference that distinguishes English regular and irregular verbs (video). For example, note the difference in the way the following verbs form the past tense:
Today, I walk.
Yesterday, I walked.
This is the regular way past tenses are formed in English. The suffix -ed (you can think of the -ed here as the equivalent of a tense formative) is added to the verb. This corresponds to the first aorist in Greek.
Today, I hold the baby.
Yesterday, I held the baby.
Note the past tense of “hold” is not “holded“. Instead of adding -ed to the verb, the spelling of the verb changes. This corresponds to a second aorist in Greek. First aorist verbs (or “regular aorists”) are identified by the tense formative σα (just as the -ed suffix on English verbs). An easy way to know if a given verb is first or second aorist is to find that verb in MBG. Then check and see if the stem is spelled the same in all the different tenses.
| λυω – I loose | present tense |
| ελυσα – I loosed | aorist tense | Note: the stem (in red) is spelled the same in both the present and aorist tense. |
| ἀκούομεν – we hear | present tense |
| ἤκουσαμεν – we heard | aorist tense | Note: the stem (in red) is spelled the same in both the present and aorist tense. The first letter changed because of the augment. |
Second aorist verbs (or “irregular aorists”) don’t take a tense formative. Instead, they change their spelling. λαμβανω is an example of such a verb.
| λαμβανω – I receive | present tense | Note: the stem here is λαμβαν- |
| ελαβον – I received | aorist tense | Note: the stem has changed to λαβ- |
| ερχομαι – I come | present tense | Note: the stem here is ερχ- |
| ηλθον – I came | aorist tense | Note: the stem has changed to ηλθ- |
Here is the full paradigm of λαμβανω, common verb that is a second aorist:
| Present active: | Aorist active: |
| λαμβάνω – I receive
λαμβάνεις – you receive λαμβάνει – he/she/it receives λαμβάνομεν – we receive λαμβάνετε – you receive λαμβάνουσι – they receive |
ἔλαβον – I received
ἔλαβες – you received ἔλαβεν – he/she/it received ἐλάβομεν – we received ἐλάβετε – you received ἔλαβον – they received |
See also the aorist passive and a gnomic aorist.