The Classical Slith verb is an exceedingly subtle creature. It can be conjugated into an incredible variety of forms, and each one was entirely available for use in everyday conversation at the dawn of the Classical Slith period. Some forms gradually fell out of use over the course of history until the language became Modern Slith, but before that, this was the standard conjugational system considered ideal for writing and speaking for several centuries.

The basic principle is this: every verb has a stem that remains completely unchanged throughout all conjugations (a feature unique to the classical tongue in the history of slith speech: there are no irregular verbs). The verb stem conjugated here is hess-, the stem "to speak." To this stem are added suffixes that indicate a variety of things about the action of the verb. First are person, number, and voice.

Person and number (familiar to speakers of modern European languages) express the subject of the verb. Classical Slith (like Spanish, Italian, etc.) has three persons and two numbers: first, second, and third, and singular and plural, respectively. Classical Slith is pro-drop (like Latin or to some extent the Slavic languages), which means that if the subject does not have to be stated, it most often won't be.

Voice expresses the relationship of the subject to the action of the verb. The active voice indicates that the subject is performing the action of the verb ("I hit the ball"). The passive voice indicates that the subject is receiving the action of the verb ("The ball was hit"). The middle voice (as in classical Greek) expresses that the subject was either the direct object of the action ("I hit myself") or performed the action for his or her own benefit ("I hit the ball for myself" — more likely, "I bought myself a sword").

Person, number, and voice are indicated by endings suffixed to the verb, which are called personal endings, as shown in the table below. (For the sake of creating real verbs, I've inserted tense vowels as well, which is the next topic.)

Tense expresses the time when an action occurs: past, present or future. It functions in almost exactly the same way as it does in English. It is indicated by a tense vowel inserted right before the personal ending. The tense vowels are: a for present, o for past, and e for future).

Mood expresses the degree to which the action expressed is real. Classical Slith has four (vaguely resembling classical Greek's four moods). Broadly speaking, the indicative used for real actions that either did happen, are happening, or will happen. These are the forms we have seen so far. The subjunctive is used for hypothetical actions near to reality or present in the speaker's mind. The optative is used for hypothetical actions that are unlikely or imagined by someone other than the speaker. The imperative is used for actions that the speaker would like to occur.

The moods are formed by modifying the tense vowel: a subjunctive lengthens, an optative adds -i before the personal ending, and an imperative adds -e before the personal ending. As you can see, the moods necessitate extremely clear vowel pronunciation, especially to differentiate between an optative and an imperative.

English does not have direct equivalents for many of these forms. "If I speak [now, and it is likely that I will, but I am not currently]" would be expressed by is hessām. It is an event regarding the present, so it takes the present tense. It is an action that is not taking place (I am not speaking right now), so it is imagined; therefore it takes either the subjunctive or the optative. It is considered likely, so it takes the subjunctive. "If I speak [now, and it is not likely that I will, and I am not currently]" would be expressed by is hessaim, optative because it is not likely. "Let it be that I speak" would be expressed by hessaem, an imperative because it is a command. (The more normal imperative for English speakers would be hessaes, that is, "Speak!")

Aspect indicates the frequency or duration of the action expressed in the verb. Classical Slith has three aspects (rather like the Polish verbs of motion, such as iść, except that all aspects can occur in all tenses). The forms so far are called the perfective forms. The perfective expresses one-time action. That is, "I speak the speech" would be hesson hessam.

However, if the action takes place over a long period of time and the emphasis is on continuing to do the action, rather than doing it and finishing it, the verbal aspect is durative, and a suffix is used to indicate that. The durative suffix is -akh, and it is inserted before the tense vowel and personal ending. Thus, "I am speaking the speech" would be hesson hessakham.

Finally, if the action is repeated often, the aspect is considered frequentative, and the frequentative suffix is -at, marked in the same place as the durative aspect. (The categories are mutually exclusive: a verb is one of three things, perfective, durative, or frequentative, but never two or all three.) Thus, "I speak the speech [on Thursdays]" would be hesson hessatam (although the sliths did not have a concept of Thursdays with which to translate).

For emphasis, the vowel in the aspect suffix may be lengthened. Thus, "I often speak the speech" would be hesson hessātam.

It is very important to note that, although the perfective form is the least marked form, it still is a form. It is not a default that serves the function of all three. It is a particular form. That is the reason that some people sometimes suggest that the indication of the perfective aspect is a "zero ending": it is an ending that consists of no letters. This is true of another form later, as well.

Not to be confused with perfective aspect, Classical Slith also has a perfect aspect. This expresses actions prior to specified times, equivalent almost exactly to the tense formed with the auxiliary verb have in English. The past perfect expresses actions that occurred prior to some other action in the past, for example. The future perfect expresses actions that occurred prior to some other action in the future. The present perfect expresses actions that have occurred prior to the present. Normally these actions also have consequences for the time period to which they are referring, which is the different between the present perfect and a past tense.

The perfect aspect is formed by adding the suffix -ith before all other suffixes. Thus, "I have often spoken" would be expressed by hessithatam. The implication might be that it is appropriate for me to speak again, perhaps. It is a past action with present consequences. Also, "I had spoken [before he spoke]" would be expressed by hessithom. The implication might be that therefore no one believed him, because I spoke first.

For emphasis, the vowel in the perfect suffix may be lengthened. Thus, "I have already spoken" would be hessītham.

As above, the non-perfect form is a form, just as the perfect is. It simply has a zero ending; it will not serve the function of the perfect in places where the perfect is required. (See the note on the perfective form above.)

For each of these tenses, moods, and aspects, there are also several verbals. The participle is an adjective that describes someone who is doing the action of the verb. The gerund is a noun expressing the act of doing the action of the verb. The infinitive usually expresses the action of the verb in a more general sense.

The participle is formed with endings that change gender and number to match the person being described, which works just like an adjective. The gerund is formed with a simple ending. The infinitive is also formed with simple endings.

An example of the participle is: "The man, having spoken [before], spoke [again]," expressed by ksēvoss hessithathōs hessoth. This might be considered nearer in English to "The man who had spoken before spoke again." The gerund might be seen in the following sentence: "Speaking well is noble," expressed by Hessashoss vonein kāle bitath. The infintive may be seen here: "I want to speak," expressed by Fōlam hessaden.

Obviously, a full inflectional chart for a Classical Slith verb would be absurdly long and complicated, so I will not write that here, but from these tables, one can build forms. It is also obvious that sliths could express a great deal with endings that English normally would use auxiliary verbs and adverbs to express. For example, when in English we say, "He should have been seen often" (i.e. in public, before he ran for office, but he wasn't likely to), sliths might simply say, "Vīdithatoitos," a verb in the form: third person, singular number, past perfect tense, passive voice, frequentative aspect, optative mood!

One should avoid the temptation of English-speakers simply to default to the present active indicative perfective non-perfect. Each of these considerations (person, number, voice, tense, aspect, mood, and perfect-ness) is a serious consideration in Classical Slith — they really did speak like this! So in order to be understood, one should give a great deal of thought to one's verbs.

Verbs are built in this order: stem-perfect aspect marker-aspect marker-tense vowel-mood marker-personal ending/verbal marker. Thus, as above, vīdithatoitos.