Causal conjunctions join two propositions to show a relation of motive and result. One proposition presents the fact, and the other explains why it happens. In It is raining because there are clouds, the main part says what happens and the cause gives the reason. This type of linkage appears a lot in explanations, answers and everyday comments. It also serves as a basis to understand other relationships between sentences, such as those that appear in Coordinating Conjunctions and Subordinating Conjunctions.

Porque introduces the direct cause of an idea and is the most common and neutral form. The basic structure is main clause + porque + cause clause. I don't go out because I am tired shows the decision first and then the motive. Because answers well to questions with why? and works in conversation, everyday writing and simple explanations. In practice, it appears when the cause comes after the fact it explains, as in We canceled the meeting because many people were missing.

Neutral use of the direct cause

Usage	Explanation
Basic explanation	Use because when you want to give the most direct cause of an idea without sounding formal or pretentious.
Answer to a question	Use because when you answer a why and want to give a clear and simple reason.

Como places the cause before the result. The structure is como + cause clause + main clause. Como hacía frío, cerramos la ventana presents the motive first and then the action. This position gives more weight to the cause and sounds natural when the speaker wants to prepare the idea before saying what happened. Unlike porque, como opens the sentence and is not used to answer only a question of motive. In explanatory texts, this ordering helps to chain ideas clearly.

Cause at the start of the sentence

Idea
Use como at the beginning when the cause appears before the result.
The cause with como usually goes before the consequence in the sentence.

Pues introduces an explanation with a more written, careful or formal tone. It usually appears after the main idea: main clause + pues + cause. No aceptó el cargo, pues no quería mudarse keeps the cause tied to the previous statement. Compared to porque, pues sounds less conversational and more suitable for writing, speeches or arguments. It can also appear in a brief pause within the sentence, where the explanation is added as a deliberate justification rather than a spontaneous answer.

Formal and written use of pues

Usage	Explanation
More careful explanation	Use pues when you want to give an explanation with a more formal tone than because.
Justification in written text	Use pues when the cause sounds more literary or more typical of written text.

Causal conjunctions explain the motive; consecutive connectors show the result. In He is tired because he walked a lot, because marks the cause. In He walked a lot, so he got tired, so marks the consequence. The decision depends on which part you want to present as the basis for the other. If the focus is on the motive, use a causal such as porque, como or pues. If the focus is on the effect, use a consecutive connector. This difference is essential to connect ideas well in dependent clauses and in argumentative sequences, such as those related to Consecutive Conjunctions and other logical relations of Spanish.

Difference between cause and effect

Idea
Causal conjunctions show the motive of something and not the result.
Consecutive connectors present the consequence and not the cause.
Do not confuse porque with connectors that express the final effect.

A causal can be limited to explaining a situation or can justify a decision. In Está en casa porque llueve, the sentence only explains a state. In No salgo porque llueve, the cause also justifies the decision not to go out. When the cause accompanies a fact already occurred or a situation, the relation is explanatory. When the cause presents the motive for an action, the relation is justificatory. This difference helps interpret the full meaning of the sentence and choose the appropriate structure within Adversative Conjunctions, Correlative Conjunctions and the other logical relations of Spanish.