The verb translated as "can" or, in the negative, as "cannot" is not a helper verb as it is in English. Translating it as "can" is very misleading. In English, it means primarily means "having the ability" but it is also used to mean "having permission." The Greek word is different, both in how it is used and how its meaning connects with other words.
The verb translated as "can" is dynamai (δύνμαται), which means means "to have power by virtue of your own capabilities," "to be able," and "to be strong enough." Jesus uses it in sixty-one verses. This is the active verb here, not a helper verb. It takes an infinitive as "have the ability to do something." It is often used in the middle voice, indicating someone having the power within themselves, from their own abilities. The root of this word is the source of our words "dynamic," "dynamo," and "dynamite."
This verb is related to both a noun and adjective from the same root. The noun is dynamis (δυνάμις) that means "power," "might," "influence," "authority," "capacity," "elementary force," "force of a word," and "value of money." Elemental forces are forces such as heat and cold. Jesus uses it in sixteen verses. The Bible translates it as "power," "mighty works," "strength," and "miracle." Another Greek word, exousia, is also often translated as "power," but it has the sense of authority over others, people and laws. Dynamis is not this type of social power as much as personal power. The related adjective, dynatos, means "strong," "mighty," "possible," and "practicable." Jesus uses it in nine verses.
Jesus will often use the verb form, dynamai, with other words, such as exousia, which relate to the use of power. He also uses it in relationship to words that give someone power.