Finnish has four moods for verbs:
The indicative mood has no suffix, though indicative forms have person suffixes like other verb forms. However, note that the stem used may differ from the stem variant in the infinitive. We have e.g. the infinitive tulla (to come), where tul is the stem and la is the suffix, and the indicative form tulen (I come), where tule is the stem and n is the person suffix.
The imperative might be said as having the mood suffix kO, but the suffix really varies. In the most common person form, 2nd person singular, the imperative coincides with the normal verb stem in writing, but in pronunciation, it participates in boundary gemination. Thus, the imperative of the verb with the stem mene- (to go; infinitive: mennä) is written simply mene, but e.g. the words mene pois are pronounced as menep pois in standard language. The 2nd person plural has the suffix kaa or kää, and the preceding vowel is omitted for many verbs. E.g., katsokaa, menkää (from mene-). The 3rd person has koon or köön in singular, koot or kööt in plural, e.g. katsokoon “let him/her watch”. The 1st person plural has the suffix kaamme or käämme, e.g. katsokaamme, but in modern language, it is rare. Finally, the 4th person form has suffixes like ttakoon, e.g. katsottakoon.
The conditional has the suffix isi. If the stem ends with e, this vowel is omitted before the conditional suffix, e.g. olisin (I would be), from ole- (to be, infinitive olla). In colloquial language, 3rd person singular often lacks a final vowel, e.g. olis instead of the standard olisi and 4th person forms like oltaisiin are usually shortened even more: oltais.
The potential has the suffix ne. When the stem ends with e, this vowel is omitted before the potential suffix, e.g. mennet (you will probably go), from mene- (to go, infinitive mennä). This loss of e could produce a consonant combination of ln, rn, or sn, but these appear as assimilated to ll, rr, or ss. For example, for tule- (to come), the potential 1st person singular is tullen (I will probably come). An additional change (loss of k) appears in verb stems ending with kse, e.g. juosta : juoksen : juossen. All these assimilated forms are rare, and they are difficult to recognize even to native speakers.
Only the indicative has a simple past tense form, for example katsoin (I watched). For the conditional and the potential, the auxiliary verb olla is used, in the conditional or potential form, together with the past participle of the main verb. Examples: olisin katsonut (I would have watched), lienen katsonut (I probably watched). The imperative has a similar form, such as olkoon katsonut, but its meaning is special. For example, olkoon hän tehnyt mitä tahansa (literally, “let he/she done whatever”) means “no matter what he/she has done”.