Whether or not the letters thus occurring together form a diphthong or digraph will depend on the derivation of the word, thus in _cat-head_ (verb), a nautical term, _th_ is not a digraph but in _ca-the-dral_ _th_ is a digraph, as is usually the case with these two letters.

You would not say _cat-hed-ral_.
Two vowels, or a vowel and a diphthong, coming together but sounded separately belong to separate syllables.
_A-or-ta_, _co-op-er-ate_, but _coop-er-age_, _moi-e-ty_.
Do not end a syllable with (_a_) _c_ or _g_ when soft, _en-ti-cing_, but _dic-tion_, _wa-ges_ but _wag-on_.
(_b_) _t_, _s_, _z_, _c_, _sc_, _g_, and _d_, when followed by _i_ or _e_ giving the sound of _sh_; _ra-tion-al_, _o-cean_, _re-gion_, _as-cen-sion_.
(_c_) _d_, _s_, _t_, and _z_ when followed by _u_ giving the sound of _ch_, _sh_, _zh_, or _j_, _cen-sure_, _sei-zure_, _na-ture_, _ver-dure_.
Do not begin a syllable with (_a_) _x_ with the sound of _ks_ or _gs_, _anx-ious_, _ex-act-ly_.
(_b_) _r_ preceded by _a_ or _e_; _par-ent_, _av-er-age_, but by exception, _pa-rent-al_.
(_c_) Single _l_, _n_, or _v_, followed by _i_ with the sound of _y_ consonant; _fol-io_ (_fol-yo_), _gen-ius_ (_gen-yus_), _sav-ior_ (_sav-yor_).
Prefixes and suffixes are generally separated, _yel-low-ish_, _eat-able_, _pre-lude_.

This last word is sometimes pronounced _prel-ude_ and this pronunciation has some dictionary support, but it is objectionable.
A consonant or digraph between two sounded vowels usually joins the following vowel, _rea-son_, _no-ti-fy_, _mo-ther_.
When two or three consonants capable of beginning a syllable come between two sounded vowels they may all be joined to the following vowel.
(_a_) When the preceding vowel is long and accented; _en-a-bling_, _He-brew_, _i-dler_.
(_b_) When the following vowel is an accented syllable; _o-blige_, _re-dress_.
When two or three consonants capable of beginning a syllable come between two sounded vowels one may be joined to the preceding vowel.
(_a_) When the vowel is short; _tab-let_, _res-cue_, _mus-ket_.
(_b_) When the consonants are _st_, _str_, or _sp_, if either the preceding or following vowel is accented; _mis-tress_, _aus-tere_, _oys-ter_, _sus-pect_.
When a consonant is doubled (not forming a digraph) the two are generally separated; _beg-gar_, _bril-liant_, _cun-ning_.
The old-fashioned method of oral spelling by syllables _m-a-s-mas-t-e-r-ter-master_ will be found extremely useful in teaching correct syllabication.

It is recommended that constant use be made of it in spelling drill.
ACCENT When a word consists of two syllables one of them receives more stress of voice than the other.

This stress of voice is called accent.