Silent E
A final E that makes no sound of its own still does work. Knowing which job it is doing tells you whether a word needs one.
The rule
A final silent E is part of the spelling, not a leftover. It often lengthens the vowel before it (hat, hate); where it does not, it may be keeping a C or G soft (dance, bridge) or standing in because English does not end a word in V (have).
The best-known job is the vowel before it: hat and hate, rid and ride, cop and cope, cut and cute. With the E, the vowel usually says its own name.
Two other jobs explain words the first one does not. After a C or G, a final E often keeps the letter soft: dance, practice, bridge, knowledge. And English does not end a word in V, so have, give and love take an E that does nothing to the vowel.
The E usually drops before an ending that starts with a vowel (hope, hoping; love, lovable) and stays before one that starts with a consonant (hope, hopeful; manage, management).
The other direction
A final silent E is there for a reason — a long vowel, a soft C or G, a word that cannot end in V. Where none of those applies, the word usually ends at its last consonant.
That is the miss in develope, and the reason envelop, the verb, and envelope, the noun, are different words.
Where it stops holding
The ending rule bends to keep a C or G soft: notice, noticeable; change, changeable; courage, courageous.
And some words keep an E that does none of the three jobs, usually in an unstressed final syllable: definite, promise.
Background
A final E carries no sound and still carries information, which is the kind of letter pattern readers mostly pick up without being taught. The research on that is on how people learn to spell.
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