English is often considered difficult to learn because it is a morphophonemic language with a deep orthography—meaning its spelling system reflects both sounds (phonemes) and meaningful word parts (morphemes), rather than having a simple one-to-one sound–letter correspondence.
English spelling preserves both morphemes (units of meaning) and phonemes (units of sound). For example, in the words sign, signal, and signature, the spelling sign- stays consistent to show meaning (“mark” or “indicate”), even though its pronunciation changes:
- sign /saɪn/
 - signal /ˈsɪɡnəl/
 - signature /ˈsɪɡnətʃɚ/
 - This morphophonemic consistency helps show relationships in meaning but makes pronunciation unpredictable.
 
A deep orthography means the connection between letters and sounds is complex and often inconsistent. Unlike a shallow orthography (such as Spanish, where spelling closely matches pronunciation), English spelling reflects centuries of linguistic change, borrowing, and historical layers.
For instance, the sound /iː/ can be spelled many ways:
- see, sea, scene, seize, machine, people
 
Each reflects different origins (Germanic, French, Latin, Greek), leading to varied spellings for the same sound.
In English, one letter or grapheme can represent multiple sounds, and one sound can be spelled many ways.
For example, the long-a sound /eɪ/ appears in:
- make, rain, day, they, great
 
And the letter c can represent different sounds:
- /k/ in cat,
 - /s/ in cent.
 
In short: English spelling evolved to preserve meaning and historical origins, not just sound. This morphophonemic and deep orthographic structure makes it richer and more expressive—but also challenging for learners who expect straightforward sound-letter rules.