Internal and η- Augment

Most of the "irregular" pasts that trip up intermediate learners are not irregular stems at all — they are ordinary stems with the augment in an unexpected place or in an unexpected shape. Once you can see the augment for what it is, verbs like κατάλαβα, υπέγραψα, ήθελα and ήρθα stop looking like exceptions to memorise and start looking like the same rule applied one layer down. This page covers the two cases where that happens: the internal augment on compound verbs, and the η- augment on a small set of high-frequency verbs. For the ordinary front augment, start with the augment in the aorist.

Compound verbs put the augment inside

A large slice of the Greek vocabulary is built from a prefix + verb: κατα- + λαβαίνω, ανα- + βαίνω, υπο- + γράφω. When such a verb goes into the past, the augment does not jump to the front of the whole word. It stays where it historically belonged — at the seam between the prefix and the stem.

The cleanest way to see it is to build the compound past in two steps: take the simple verb's past, then bolt the prefix on the front.

• υπογράφω "sign" = υπο- + γράφω. The past of γράφω is έγραψα. Prefix it: υπ(ο) + έγραψα → υπέγραψα (the -ο of υπο- elides before the augment's ε-). The stress sits on that internal έ.
• ανεβαίνω "go up" = ανα- + βαίνω. The past of βαίνω is έβηκα. Prefix it: αν(α) + έβηκα → ανέβηκα.
• κατεβαίνω "go down" → κατ(α) + έβηκα → κατέβηκα.

The single most important thing to remember: the augment is internal, never external. You say ανέβηκα, not ×εανέβηκα; υπέγραψα, not ×εϋπόγραψα. Putting the augment at the front of a compound is the classic mistake, and it is always wrong.

Two ways the internal augment surfaces

Compounds split into two behaviours, and the split is essentially one of register.

The learned/formal type keeps a visible internal ε-. Verbs inherited as a fixed unit from older Greek — especially in careful writing, the news and officialese — show the ε- plainly, with the stress on it: υπέγραψα, προέβλεψα (προβλέπω "predict"), απέδειξα (αποδεικνύω "prove"), συνέλαβα (συλλαμβάνω "arrest"). These forms are (formal); you meet them constantly in reading even if you rarely build one from scratch.

The everyday type drops the ε- and simply retracts the stress onto the prefix. In demotic Greek most common compounds are long enough already, so they need no ε- at all — the past-tense stress just falls back into the prefix zone: καταλαβαίνω → κατάλαβα (κα-τά-λα-βα), περιμένω "wait" → περίμενα (πε-ρί-με-να), προλαβαίνω "have time / catch" → πρόλαβα, ξεχνάω "forget" → ξέχασα. There is no ε- here to see, but the mechanism is the same one — the augment slot is internal, and it is realised as stress retraction rather than a vowel.

The η- augment

A second surprise is the shape of the augment on a small, very frequent set of verbs. Instead of ε-, they take η-. Historically this is an ε- augment that fused with a following vowel and came out as η; synchronically you should just learn these as the verbs whose past begins with η-:

A precision point worth flagging honestly: two of these are technically imperfects and two are aorists. θέλω and ξέρω have no everyday separate aorist — ήθελα and ήξερα do the work of the whole past — while ήπια and ήρθα are genuine perfective aorists (single, completed: I drank it, I came). The reason they all belong together is not their aspect but their augment: the η- is what makes them look odd, not the stem underneath.

The verb έρχομαι also has a (formal) aorist ήλθα, built on the same η- augment, which you will meet in written and elevated Greek beside the everyday ήρθα. These forms shade into outright suppletion — where the past stem is a different root altogether — and the full set of those is on irregular and suppletive aorists.

A worked example: building a compound past

Suppose you know the verb γράφω but meet υπογράφω "sign" for the first time and need its past. Work in three moves:

1. Strip the prefix. υπογράφω → prefix υπο-
   • base γράφω.
2. Form the base past. The aorist of γράφω is έγραψα (augment + perfective stem γραψ-).
3. Re-attach the prefix, eliding where the vowels meet: υπ(ο) + έγραψα → υπέγραψα.

The same recipe gives προ- + έβλεψα → προέβλεψα, and δια- + έκρινα → διέκρινα (διακρίνω "distinguish"). You are never inventing a new past; you are augmenting a base you already know and letting the prefix ride on the front.

Common Mistakes

1. Fronting the augment on a compound. The augment is internal; it never sits before the prefix.

2. Using ε- where the verb wants η-. θέλω builds its past with η-, not ε-.

3. Regularising ήρθα to ×έρθα. έρχομαι has the η- augment (everyday ήρθα, formal ήλθα).

4. Giving πίνω a plain ε- augment. Its aorist is ήπια.

Key Takeaways

• On compound verbs the augment is internal, at the prefix–stem seam: υπέγραψα, ανέβηκα, κατάλαβα — never ×εανέβηκα.
• It surfaces two ways: a visible internal έ- in learned/formal compounds (υπέγραψα, προέβλεψα, συνέλαβα), or plain stress retraction onto the prefix in everyday ones (κατάλαβα, περίμενα, πρόλαβα).
• A small, frequent set of verbs takes an η- augment: ήθελα, ήξερα (imperfects) and ήπια, ήρθα (aorists).
• Build a compound past by augmenting the base verb and re-attaching the prefix (γράφω → έγραψα → υπέγραψα).
• Most "irregular" pasts are really augment oddities, not stem oddities — check the front of the word first.