Use the prolative case suffix -tse to express the route taken or the medium used for communication. It answers the question "by what way?" or "via what?" and often translates to English as "by" or "via".
Forming the Prolative Case
Add the suffix -tse to the noun. It is typically attached to the noun's plural stem, meaning you will often see the plural marker -i- right before the ending, even if the meaning is strictly singular.
For example, puhelin (phone) uses its plural stem puhelimi- to become puhelimitse (by phone), and kirje (letter) becomes kirjeitse (by letter). Some words, like sähköposti (email), attach the suffix directly to the singular stem to become sähköpostitse.
Communication Mediums
This case is highly common when discussing how information is delivered, especially in customer service or official contexts.
| We sent the tracking code by email. | Lähetimme seurantakoodin sähköpostitse. |
| The customer service is easy to reach by phone. | Asiakaspalvelu on helppo tavoittaa puhelimitse. |
| I do not know anything about the complaint, because he sent it by letter. | En tiedä reklamaatiosta mitään, koska hän lähetti sen kirjeitse. |
Physical Shipping Routes
You will also use -tse to describe physical travel or shipping routes. When attached to terrain types like maa (land) and meri (sea), the plural stems are mai- and meri-, giving you maitse (by land) and meritse (by sea).
| Is the delivery time for express delivery shorter by sea or by land? | Onko pikalähetyksen toimitusaika lyhyempi meritse vai maitse? |
Customer Service and Official Contexts
The prolative is particularly useful for formal instructions, requests, or complaints. It pairs well with conditional statements and professional correspondence.
| If the package gets damaged, you can request a return by email. | Jos paketti vaurioituu, voit pyytää palautusta sähköpostitse. |
| We request contact by email. | ”Pyydämme yhteydenottoa sähköpostitse.” |
