Islandish has a way to express probability and certainty of a verb action with special grammatical moods.
Indicative is the neutral mood, where the probability of an action is not expressed.
Potential expresses an action, which is probable, but not certain.
Commissive expresses certainty, personal commitment of the speaker to the truth of the statement.
Conditional expresses an action which depends on a condition.
The moods are constructed using the auxiliaty verb "viti" in various tenses and aspects. The aspect of the action is expressed by the aspect of the full verb. The full verb itself is:
in present indicative for the present tense
in infinitive for the future tense
in past participle for the past tense.
Potential
The potential mood uses the auxiliary verb in the future habitual aspect.
Dubit lokov nivrej klej. The old man is probably dying.
Vládec nivrej sprhti. The lawyer will probably lie.
Mama nivrej škopidla mnělkó. Mom has probably baken a cake.
If the full verb is the verb "viti", then the present tense form is omitted and only the future form is used:
Nivrej osprha. It is probably a lie.
Commissive
The commissive is used with the auxiliary verb in the future perfective aspect. With the commissive, the speaker promises or guarantees that the utterance is true (it can also be a threat).
Nidrej vevukla. She certainly forgot.
Sažkov nidrej breti bo de gubľadej. The present will certainly make her to fall for you.
Nidrem de lbáti. I promise I will defend you.
Nidrem gradem. I swear I say the truth.
If the full verb itself is the verb "viti", then in present, the present indicative is ommitted.
Nidrej smúgva. I swear it is a mistake. It is certainly a mistake.
The commissive is also used in reassuring questions or to to reinforce the certainty of a previous statement. In these cases and in short answers, the sole future form can be used.
Nidreš jabrsti? Nidrem! Will you really come? I will!
Došlidem čebnó vrilčetó! Nidrem! I will find the lost child. I promise.
Conditional
Conditional is formed with the past forms of the verb "viti" and the full verb in the same forms as in the above moods. The condition itself is in the indicative, potential or commissive, and is preceded with the conjuction hoka or bo.
Hoka jabrzdeš vzi čiľi, mama viha škopilti mnělkó. If you come home, mom will bake a cake.
Bo glívleš, više znaknel. If you had listened, you would have understood.
Bo práčeš, vih žárim. When you laugh, I am happy.
The conditional can be combined with the commissive and the potential, by putting the past form of "viti" in the respective aspect:
Hoka nireš gňan, videh di sažeti ľení klimček. If you are good/nice/brave, I promise I will give you a new toy.
Bo nej vručelo, vijmih šali i čiľi. If it has rained, we would probably have stayed at home.