Causal conjunctions introduce the reason, motive or explanation of what is stated in the main clause. In Spanish they usually join two propositions and establish a cause-and-effect relationship that is interpreted by context. They relate to other kinds of links such as Subordinating Conjunctions and, depending on the structure, may appear close to the Coordinating Conjunctions.

Because expresses the direct explanation and is the most frequent causal form in general language. 'Pues' also introduces a cause, but tends to sound more colloquial and can appear in medial or final position. Both forms link the cause with a sentence in the indicative mood and do not change according to gender or number, so their form is invariable.

IdeaIdea	EjemploExample
Porque introduce una explicación directa.Because introduces a direct explanation.	Llegó tarde porque perdió el tren.He arrived late because he missed the train.
Pues introduce una causa de tono coloquial.'Pues' introduces a cause with a colloquial tone.	No vino, pues estaba enfermo.He didn’t come, as he was sick.
Porque no cambia de género ni de número.Because it does not change in gender or number.	Porque explica la causa sin concordar.Because it explains the cause without agreement.

'Puesto que' expresses a more formal justification and is often used in written or careful registers. 'Ya que' presents a motive evident or shared by speaker and listener. These causal conjunctions are usually followed by the indicative mood and relate to the explanatory links that also study the Subordinating Conjunctions.

IdeaIdea	EjemploExample
Puesto que introduce una justificación formal.Puesto que introduces a formal justification.	Puesto que llovía, cancelamos.Puesto que llovía, cancelamos.
Ya que señala un motivo evidente.Ya que indicates an evident motive.	Ya que viniste, quédate a cenar.Ya que viniste, quédate a cenar.
Ya que mantiene un tono menos directo que porque.Ya que maintains a less direct tone than because.	Ya que sabemos la causa, decidimos actuar.Ya que sabemos la causa, decidimos actuar.

As at the beginning of the sentence, it introduces a known or assumed cause and is usually placed before the main proposition. When it opens the sentence, it normally carries a comma after the causal subordinate clause. This usage can sound more formal or literary in some dialects and is clearly distinguished from Comparative Conjunctions, where como does not express a cause.

IdeaIdea	EjemploExample
Como al inicio expresa causa conocida.As at the start expresses a known cause.	Como no estudiaste, suspendiste.As he was not studying, you failed.
Como inicial lleva coma después de la causa.As initial carries a comma after the cause.	Como hacía frío, cerramos la ventana.As it was cold, we closed the window.
Como inicial puede sonar más formal.As initial can sound more formal.	Como llegó temprano, pudo ayudar.As he arrived early, he could help.

'Debido a' and 'a causa de' introduce a cause followed by a noun or noun phrase, not by a full verbal clause. 'Por culpa de' expresses a negative cause or a responsibility that is attributed to someone or something, and for that reason it can feel strong or accusatory. 'Gracias a' indicates a favorable cause or beneficial motive, while 'por culpa de' is usually avoided in delicate contexts.

IdeaIdea	EjemploExample
Debido a va seguido de sustantivo.'Debido a' is followed by a noun.	Cancelado debido a la nieve.Cancelled due to the snow.
A causa de va seguido de sustantivo.'A causa de' is followed by a noun.	Faltó a clase a causa de la tormenta.Missed class due to the storm.
Por culpa de marca causa negativa.'Por culpa de' marks a negative cause.	Falló por culpa del técnico.Failed due to the technician's fault.
Gracias a marca causa positiva.'Gracias a' marks a positive cause.	Ganó gracias a su esfuerzo.Won thanks to their effort.

Punctuation helps identify the causal relation and avoid ambiguities. When 'como' opens the sentence, it is usually written with a comma after; when 'porque' appears inside the sentence, it is normally not separated by a comma. These conjunctions do not inflect for gender or number, and the causal subordinate is constructed in most cases with the indicative mood.

IdeaIdea	EjemploExample
Como inicial suele ir seguido de coma.As initial, it is usually followed by a comma.	Como estaba cansado, se fue temprano.As he was tired, he left early.
Porque medial suele ir sin coma.'Porque' in medial position usually goes without a comma.	Se fue temprano porque estaba cansado.He left early because he was tired.
Las conjunciones causales son invariables.The causal conjunctions are invariable.	Porque y pues no cambian de forma.'Because' and 'Pues' do not change form.
La causa suele expresarse con indicativo.The cause is usually expressed with the indicative mood.	Puesto que llueve, nos quedamos.Puesto que llueve, nos quedamos.

The choice among 'porque', 'puesto que', 'ya que', 'como', 'pues', 'debido a', 'a causa de', 'por culpa de' and 'gracias a' depends on the register, the level of explicitness, and the evaluation of the cause. Recognizing the difference between 'por qué' in questions and 'porque' in answers helps avoid common writing errors. With these forms, the causal relation is interpreted with precision in both oral and written comprehension, as in the structures treated in the Consecutive Conjunctions and the Correlative Conjunctions.