The aorist, or geniş zaman (broad tense) in Turkish, very roughly corresponds to the English present simple. Its formation is quite irregular, and its usage is also quite difficult to grasp, making this tense quite a challenge for new learners.
In all multi-syllable verbs ending in consonants, the suffix -ır/ir/ur/ür is used, obeying 4-way vowel harmony, followed by the usual personal endings.
Verb stem + appropriate form of ır + personal ending
Most single-syllable verbs take the ending -ar/er in the aortist, but there are around 16 irregular verbs ending in r, l or n that take -ır/ir/ur/ür instead, a list of which is found below. The two verbs tatmak,etmek and gitmek undergo consonant voicing, as in the present tense.
Verb stem + appropriate form of ar + personal ending
While this list of exceptions is based on the official Turkish dictionary by TDK, the actual forms used by speakers may vary.
Speakers tend to avoid the three exceptional verbs ending in n. The double passive forms denilmek and yenilmek are used instead of denmek and yenmek, and sanmak is often replaced with its synonym zannetmek in the aorist, except for the idiomatic phrases sanırsam and sanırım, reducing the list size down to 12.
The negative form of the aorist is -ma(z)/me(z), very different from the affirmative form. -mez version of the suffix is most often pronounced /mæz/ rather than /mez/, the e being pronounced similar to the a in trap.
Verb stem + appropriate form of ma(z) + personal ending
While the present tense -yor is used for habitual events directly witnessed or observed by the speaker, the Aorist is used to express general rules and principles instead.
Tavşanlar otla beslenir. Rabbits eat plants.
İman mutluluk getirir. Faith brings happiness.
Burada sigara içilmez. Smoking isn't allowed here.
Ali çok konuşmaz. Ali doesn't speak that much.
Turning these into the Present would turn them into general observations, rather than definitive rules.