Um- is used for verbs that already happened and is currently happening. It can only be used with verbs that begin with a vowel when used as prefix. Past tense: Um + verb (root word) Progressive: Um + first syllable of verb + verb (root word) <<< repeating the first syllable of the verb only applies when um- is used as a prefix Umalis = left, Umaalis = leaving Umiyak = cried, wept; Umiiyak = crying Umakyat = climbed, Umaakyat = climbing Umikot = turned, Umiikot = turning *The words below involves a different set of rules but I gave this example just to show how um- affects the tense. I'll explain more about this form in another topic if you want. Kumain = ate, Kumakain = eating Kumilos = moved, Kumikilos = moving Mag- is usually used for verbs in the present or future tense. May be used with verbs that begin with a vowel or a consonant. Mag- can only be used as a prefix. Present tense: Mag + verb (root word) Future tense: Mag + first syllable of verb + verb(root word) Mag-alis = remove, Mag-aalis = will remove Maghugas = wash, Maghuhugas = will wash Mag-isip = think, Mag-iisip = will think Magsalita = speak, Magsasalita = will speak Note: Adding um- or mag- to the same root word completely changes the meaning of the word. Root word: alis = go Umalis = left (went), Mag-alis = remove Root word: akyat = climb Umakyat = climbed, Mag-akyat = carry (bring, transport to a higher place) I'd be happy to elaborate further if you want to know more.

The easiest way to think about this is that mag- verbs describe actions which involve an exterior object, while actions described by um- verbs don't. Examples: Ngumiti ka na! = Smile! Umiisip ako = I am thinking Lalakad na kami = We will leave now Nagtanong siya sa guro = He asked the teacher Nag-aahit ang barbero sa kanya = The barber is shaving him Magbabayad ako ng kuryente mamaya = I will pay the electric bill later Additionally, mag- verbs express deliberate action, whereas um- verbs can express actions that involuntary. This is usually done with adjective roots to show the actor taking on a given attribute. Examples: Lumalaki na ang bata = The child is growing / getting bigger Gumanda na siya = She became more beautiful Lalakas ka pa kung tuloy-tuloy ang training mo = you will get stronger if you continue your training Hope that helps!

Wow, that got really messed up... Lemme post that as an answer instead.

The easiest way to think about this is that mag- verbs describe actions which involve an exterior object, while actions described by um- verbs don't. Examples: Ngumiti ka na! = Smile! Umiisip ako = I am thinking Lalakad na kami = We will leave now Nagtanong siya sa guro = He asked the teacher Nag-aahit ang barbero sa kanya = The barber is shaving him Magbabayad ako ng kuryente mamaya = I will pay the electric bill later Additionally, mag- verbs express deliberate action, whereas um- verbs can express actions that involuntary. This is usually done with adjective roots to show the actor taking on a given attribute. Examples: Lumalaki na ang bata = The child is growing / getting bigger Gumanda na siya = She became more beautiful Lalakas ka pa kung tuloy-tuloy ang training mo = you will get stronger if you continue your training Hope that helps!