IV

Words which in their shortest form end in _-d_, _-de_, _-ge_, _-unit_, _-rt_, _-se_, _-sr_, take the ending _-sion_; e.g., abscind, abscission; include, inclusion; emerge, emersion; remit, remission; infuse, infusion; repress, repression.

All others take the ending _-tion_.

The following are irregularities: 

adhesion assertion attention coercion cohesion crucifixion declension dimension dissension distortion divulsion expulsion impulsion insertion intention occasion propulsion recursion repulsion revulsion scansion suspicion tension version

Words ending in _-ance_, _-ence_; _-ancy_, _-ency_; _-ant_, and _-ent_, often cause confusion when carelessly written.

The following is a list of the more common words with the e form.

abducent abhorrence, -ent abluent absent, -ence absorbent abstergent abstinence, -ent adherence, -ent advertency, -ent affluence, -ent antecedence, -ent apparent appertinent appetence, -ency ardent benevolence, -ent circumference coexistence coherence, -ent coincidence, -ent competence, -ent concurrence, -ent condolence conference confidence, -ent confluence, -ent consentient consequence consequent consistence, -ent consistency constituent continence, -ent convenience, -ent corpulence, -ent correspondence, -ent currency, -ent deference delinquency, -ent dependence, -ent deponent descendent (adj.) despondency, -ent difference diffidence, -ent diffluent efficiency, -ent eminence, -ency eminent excellence, -ency excellent existence, -ent expediency feculence, -ent flocculence, -ent fluency, -ent fraudulence, -ent imminence, -ent impatience, -ent impellent imprudence, -ent impudence, -ent incipience, -ent incumbency, -ent independence, -ent indolence, -ent inference inherence, -ent intermittent iridescence, -ent lambent latency, -ent leniency, -ent magniloquence, -ent malevolence, -ent mellifluence, -ent mollient obedience, -ent occurrence, -ent omniscience, -ent opulence, -ency opulent patience, -ent pendent (adj.) pendency penitence, -ent permanence, -ent permanency pertinence, -ent pestilence, -ent poculent portent potency, -ent precedence, -ent preference prescience, -ent presence, -ent presidency, -ent proficiency, -ent prominence, -ent proponent providence, -ent prudence, -ent purulence, -ent quintessence recurrence, -ent reference refluence, -ent repellent residence, -ency resident resolvent resplendence, -ent respondent reverence, -ent sentient solvency, -ent somnolency, -ent subserviency, -ent subsidence, -ency subsistence, -ent succulent superintendence superintendency superintendent tendence, -ency transcendence, -ent transcendency transference transient transparency, -ent transplendency, -ent turbulence, -ent vicegerency, -ent virulence, -ent

Nearly all other words of this type take the a form.