Ways of saying Would/Should/Could/Must?
I know that "would" can be formed with verbs using the conditional (e.g Tendría, escribiría, etc), and that "should" can be formed with using "deber" e.g Debo hacerlo ahora = I should / ought to do it now. But what are ways of saying Could and Must? I think must can be used as tener que / hay que, but are there just any other ways of saying these? I'm pretty sure I've seen "could" be expressed by using poder in the conditional e.g "Podrías leerlo para mí? = Could you read this for me (literally would you be able to read this for me? I guess) I think what I also need to know is how to put these into the perfect tenses (e.g I would have, I should have, must have etc). Basically can any (fluent / native speaker clear this up for me?
It can be complicated but this will get you started:
Must - present tense of deber "Debo pagar mis impuestos." (It's a very strong sense of obligation)
Have to = tener que (which means more or less the same as must)
Should - conditional of deber "Debería hacer ejercicio"
Could - either conditional podría, past subjunctive pudiera, or imperfect podía (this is where it gets complicated and it depends on the context)
Must have = It looks like it's tener que haber + past participle. https://www.duolingo.com/comment/423016/You-must-have-come-here-as-a-child
Should have = This is probably similar. debería haber + past participle
Had to = indicative (tuviste que) subjunctive (si tuvieras que) - tú form
Could have = either conditional perfect (podría haber + infinitive) or subjunctive pluperfect (si pudieras hubiera + infinitive)
I'm not an expert, but this is what I've figured out so far.
Also, I think I've figured out the context thing for the word "could". "Could you take this for me?" "Podrías tomar esto para mí?". When I was a boy I could run "Cuando era un niño, podía correr". "If I could travel, I would go to Spain" "Si pudiera viajar, iría a España".