kasi and dahil have the same meaning. they both mean ' because' Mag- aaral ako kasi/ dahil may pagsusulit ako bukas - I will study because I have an exam tomorrow. Umuwi siya dahil/ kasi may sakit siya. S/he went home because s/he was sick. Dahil can also mean " due to" and "because of " Dinala siya sa pagamutan dahil sa hika. Dahil sa iyo nakapasa ako. Because of you I passed the test. S/he was hospitalised because of asthma I hope my explanations help.

I'm sorry if I flooded you with comments. It was not my intention. I'm new to italki and I still am not familiar with the interface. I couldn't find the button to delete or edit my previous comment or format it in such a way that there will be a space in between different points (start a separate paragraph). So I tried a second attempt to format my comment, to no avail. LOL this is uncomfortable.

They both mean the same, "because". "Kasi" is informal. "Dahil" is formal. Dahil is always correct to use but would sound awkward when used in some informal conversations (e.g. talking to very close friends). However, this rule is always true: when the latter part of the compound sentence (after the conjunction "because") is a dependent clause (not a complete sentence), you should always use "dahil". Example: He tripped because he ran fast. "He ran fast" is an independent clause that still conveys a complete thought when removed from the compound sentence. In this case, you can use either "kasi" or "dahil". "Dahil" is more appropriate for formal conversation/writing. Siya ay nadapa dahil tumakbo siya ng mabilis. Siya ay nadapa kasi tumakbo siya ng mabilis. He tripped because of his fast run. "His fast run" is not a complete sentence and would only make sense when part of the compound sentence. It is a dependent clause. In this case, ALWAYS use "dahil". Nadapa siya dahil sa kanyang mabilis na pagtakbo. He was wounded because when he ran fast, he tripped. "when he ran fast, he tripped" conveys a complete thought. Thus, an independent clause. You can use "kasi" or "dahil" in this case again. Nasugatan siya dahil sa pagtakbo niya ng mabilis, nadapa siya. Nasugatan siya kasi sa pagtakbo niya ng mabilis, nadapa siya.

They both mean the same, "because" (when loosely answering why questions). "Kasi" is informal. "Dahil" is formal. Dahil is always correct to use but would sound awkward when used in some informal conversations (e.g. talking to very close friends). However, this rule is always true: when the latter part of the compound sentence (after the conjunction "because") is a dependent clause (not a complete sentence), you should always use "dahil". Example: He tripped because he ran fast. "He ran fast" is an independent clause that still conveys a complete thought when removed from the compound sentence. In this case, you can use either "kasi" or "dahil". "Dahil" is more appropriate for formal conversation/writing. Siya ay nadapa dahil tumakbo siya ng mabilis. Siya ay nadapa kasi tumakbo siya ng mabilis. He tripped because of his fast run. "His fast run" is not a complete sentence and would only make sense when part of the compound sentence. It is a dependent clause. In this case, ALWAYS use "dahil". Nadapa siya dahil sa kanyang mabilis na pagtakbo. He was wounded because when he ran fast, he tripped. "when he ran fast, he tripped" conveys a complete thought. Thus, an independent clause. You can use "kasi" or "dahil" in this case again. Nasugatan siya dahil sa pagtakbo niya ng mabilis, nadapa siya. Nasugatan siya kasi sa pagtakbo niya ng mabilis, nadapa siya.