-essa (2. infinitiivi)

The second infinitive inessive is a core part of the temporal construction (temporaalinen lauseenvastike). It allows for more compact and formal sentence structures. It expresses an action that is simultaneous with the main verb, regardless of whether the main verb is in the past or present tense (though there are exceptions in certain idioms like tähän mennessä). Note that this construction cannot be used for actions that happen before the main clause; for that, you would use the past temporal construction (e.g., syötyäni).

1. Formation:
Take the first infinitive (dictionary form). Replace the final -a/-ä with -e- and add the inessive ending (-ssa/-ssä). Remember vowel harmony: words with a/o/u take -ssa, while words with front vowels ä/ö/y or only neutral e/i take -ssä.

• puhua → puhu-e-ssa (while speaking)
• syödä → syöd-e-ssä (while eating)

2. Vowel Changes and Gradation:

• If the verb stem ends in -e (Type 1 verbs like lukea), replacing the final -a with -e would result in a double vowel (lukee-). To avoid this, the first -e- (from the stem) changes to -i-, resulting in '-ie-'. Example: lukea → luk-i-essa.
• Consonant Grade: The construction uses the exact same stem and consonant grade as the dictionary form.

3. Subject Rules:

• Same Subject: If the person doing the action is the same as the main clause, you MUST add a possessive suffix. Example: Syödessäni luin. (While I was eating, I read.)
• Different Subject (Nouns): If the subject is a noun, it is put in the genitive case and no suffix is used. Example: Isän tullessa... (When father was coming...)
• Different Subject (Pronouns): If the subject is a personal pronoun, the possessive suffix marks the actor. With first- or second-person reference the genitive pronoun is optional and can add emphasis; when included, place it before the infinitive. For 3rd person subjects (hänen/heidän), the pronoun is strictly mandatory to distinguish the different-subject construction from the same-subject construction. Example: Meidän syödessämme... (While we were eating...), Hänen tullessaan... (When he/she was coming...).

4. Object Case Rule:
The object takes the exact same case it would take in the equivalent 'kun' (when) clause. Example: Lukiessani kirjaa... (While reading a book...) or Ostaessani auton... (When buying the car...). However, there is an important exception: an object in a passive second-infinitive construction normally takes the partitive (e.g., Taloa rakennettaessa, not Talo rakennettaessa).

5. Passive Form:
You can also use the passive form to mean 'while something is being done'. The passive form is created by taking the passive stem and adding -taessa/-täessä or -ttaessa/-ttäessä. Examples: tehdä → tehtäessä, sanoa → sanottaessa, and lukea → luettaessa.

6. Register:
This form is common in standard written Finnish. In everyday spoken Finnish, people usually prefer using kun clauses.

Negation and Actor Placement
Put a separate genitive actor before the infinitive: Isän tullessa..., not a detached genitive after it. This temporal construction has no ordinary negative finite-verb equivalent inside it. Use a full clause for a negative event: Kun en nukkunut, kuuntelin musiikkia (when I was not sleeping, I listened to music). The -essa form relates the times of events; it does not inherit a tense ending from the main verb.