Explicative coordinating conjunctions (conjunções coordenativas explicativas), link parts of the sentence to indicate a reason or explanation.
The most common are:
comoas (at the start of sentences)
porquebecause (in the middle of sentences)
quebecause (in the middle of sentences)
poissince (in the middle of sentences)
Examples:
Acho que estou doente, porque tenho frioI think I am sick because I feel cold
Como tenho frio, devo estar doenteAs I feel cold, I must be sick
These conjunctions are often used in combination with the imperativo verb form, as in:
Fecha a porta, pois está frioClose the door since it is cold
Prova isto, que está muito bomTaste this, because it's very good
Conjunctions That Present An Explanation

I’m trying to get my head around the difference between these. Are these three interchangeable? As, since and because kind of mean the same in English don’t they? Does como have to come of the beginning of the sentence? Thanks for your help, it really is very much appreciated.
Good question, Angela. These three are pretty much identical in terms of the idea they convey, but they are not all interchangeable. The only interchangeable conjunctions here are “porque” and “pois” – of these, “porque” is the most commonly used and it also sounds less formal than “pois”. They’re both typically used in the middle of a sentence. Unlike those two, “Como” opens the sentence, like you said. That’s just about the only difference between them.
Living in the Algarve we hear ‘pois, pois’ a lot (particularly when people are on the phone). Any ideas what the English equivalent would be when it is used in this way?
It depends on context and tone. It can be perfectly neutral or quite sarcastic. Either way, it’s comparable to “Right…”, “I see…”, “Yeah…” in English – it’s kind of a filler 🙂
Could “Que” also belong in this list? I’ve come across it from time to time in dialogue, eg “… que se prevê chuva”. How would you translate it – maybe “as” or “since”? When exactly would you use it?
Yes, in some contexts, ‘que’ can also be a coordinating conjunction, although it just as often (if not more) acts as a subordinating one. It’s comparable to ‘porque’ (because) and it’s also used in sentences where it’s adding some kind of justification to the idea presented in the first clause. For example:
– Vem cá, que quero dizer-te algo. -> Come here, because I want to tell you something.
Thanks, really helipful.