because
'cause
/kəz/ReductionElision
In real speech
What happens to the sounds
The first syllable be- disappears and the vowel weakens to /ə/: because → 'cause /kəz/.
When to use it
Constant in conversation and songs. In texts people write cuz or bc. In essays and work emails use because or since.
Casual → formal
Slang
'cause / cuz
Neutral
because
Formal
since / as
Sound notes
Reduction: unstressed words get squeezed, and their vowels turn into the neutral sound /ə/.