-s

The -s particle is an enclitic, meaning it is added to the very end of a word after all other endings. In the combinations taught here it comes last: -kos/-kös and -pas/-päs. Unlike most Finnish suffixes, it does not follow vowel harmony because it has no vowels of its own.

1. With Imperatives (Commands)
Adding -s to an imperative can make it a familiar nudge or collaborative request. Tone matters: it can also make an instruction sound insistent or patronizing. This works for both singular and plural imperatives.
• Katso! (Look!) → Katsos! (Hey, look at that!)
• Katsokaa! (Look [plural]!) → Katsokaas! (Hey, you guys, look!)

2. With Questions and -ko/-kö
When attached to question words like mikä or kuka, it adds a 'chatty' or musing quality. It also frequently stacks with the question particle -ko/-kö to form -kos/-kös, which softens yes/no questions. In modern spoken Finnish, this -kos/-kös stack is extremely commonly contracted to -ks. Note that while -kos/-kös is chatty, the contracted -ks has undergone semantic bleaching and can serve as a relatively neutral equivalent of -ko/-kö in colloquial varieties, without necessarily sounding 'chatty'.
• Mitäs kuuluu? (So, how's it going?)
• Onkos nälkä? / Onks nälkä? (Are you hungry, then?)

3. With the Passive (Suggestions)
In spoken Finnish, the -s is often added to the passive form when it is used to mean 'let's'. When -s is attached to a word ending in -n (such as the passive/suggestive -taan/-tään), the final -n is dropped. A highly common example of this is the word mites (from miten + s), as in Mites menee? (How's it going?).
• Mennään. (Let's go.) → Mennääs! (Let's head out!)

4. Register and Origin
This particle is a key part of informal speech. It is usually unsuitable in neutral formal exposition, but occurs in written dialogue, conversational prose, and deliberately personal instructions; writing itself does not prohibit it. Etymologically, -s is widely considered a historical contraction of the second-person singular pronoun sinä/sä. It functions as a distinct clitic in its own right to signal familiarity and casualness. The emphatic clitic stack -pas/-päs is formed by adding -s to -pa/-pä.

Placement: Attach -s to the question word or directive verb, normally at the beginning of the clause: Missäs avaimet ovat? and Odotas hetki. Do not append it to an arbitrary final noun. This is an early-clause host tendency, not a rule that the first written word always receives it: an introductory particle may precede the host, as in No, mitäs nyt?