Just to be clear, “tense” and “aspect” are terms applicable to English verbs. We only use these terms when we use English to explain Tagalog grammar, but Tagalog does not use these terms at all. What we use in Tagalog are just “pangnakaraan (for the past/for what has transpired)”, “pangkasalukuyan (for the present/for something that’s ongoing)”, and “panghinaharap (for the future/for what we are facing/for what is in front of us)”.
"Kumakain ako ng pizza kahapon nang dumating siya." = I was eating pizza yesterday when she arrived. [the speaker has started but not yet finished eating at a past time, hence kumakain here is not present tense]
We use “kumakain” to mean either “eat/s” or “eating”. “Kumakain” in that sentence is not the present tense “eat/s”, but the participle “eating”.
Tagalog does not have an equivalent for the English auxiliary verb “to be”. We use time indicators to determine if the statement is about the past or the present or the future. In the absence of an indicator, the default time is the present.
KUMAK
AIN ako lagi ng almus
ál. = I always EAT breakfast.
KUMAK
AIN ako. = I EAT/AM EATING.
KUMAK
AIN ak
ó habang nan
óno
ód ng TV. = I EAT/AM EATING while watching TV.
KUMAKAIN ako habang nanonood ng TV kah
apon. = I WAS EATING while watching TV yesterday.
"Kakain dapat ako ng pizza kahapon kung hindi lang sumakit ang ipin ko." = I would have eaten pizza yesterday if my teeth didn't hurt. [the speaker was contemplating on eating yesterday but the action wasn't started, hence kakain here is not future tense]
I think the translation is not correct.
The use of “kakain” and “dapat” suggest something that was planned and that was meant to happen.
So, "KAKAIN DAPAT ako ng pizza kahapon kung hindi lang sumakit ang ipin ko." would be understood as “I WAS SUPPOSED TO EAT pizza yesterday if only my teeth didn’t hurt.”. It would apply to a situation like, for example, the speaker and his friends have made arrangements to meet at a pizza restaurant. The speaker chose not to go, but his friends went ahead with the plan.
To give it that “would have” meaning, the sentence could be stated as either:
1) “Kumain dapat ako ng pizza kahapon…” = “I would have eaten pizza yesterday…”. - “Kumain” can limit the decision, to have pizza or not, and the event itself to take place entirely with the speaker.
2) “KAKAIN SANA ako ng pizza kahapon…” = “I WAS HOPING TO EAT pizza yesterday…”. The use of “sana (hopefully)” suggests uncertainty about the event. Something might eventually prevent it from happening.
"Kapag kumain kami ng pizza bukas kahit wala ka, magagalit ka ba?" = If we were to eat pizza tomorrow without you, will you get mad? [the act of eating has already been completed in the future, hence kumain here is not past tense]
Yes, “kumain” there is not in the past tense but the infinitive “to eat”. When “kapag kumain” is used, “bukas” loses its importance because the time element becomes irrelevant. “Kapag” is “if and when”, and even more of “when”. ("Kung" is "if".) What would only matter then is that the person concerned won’t be around “when” they eat pizza. So, it could also be later that same day or even in the past, if the speaker only wants to gauge how the other person is going to react when he finds out that it actually happened without him.
I would express the Tagalog sentence instead as:
"KUNG KAKAIN kami ng pizza bukas kahit wala ka, magagalit ka ba?" = IF WE WERE TO EAT pizza tomorrow even without you, would/will(?) you get mad?
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