Patrones de cognados

Spanish and English share tens of thousands of words because both languages inherited a massive Latin-derived vocabulary — Spanish directly from its Latin parent, English through Norman French and centuries of academic borrowing. The practical consequence is enormous for an English-speaking learner: once you know the suffix substitution rules, you can convert English vocabulary into educated Spanish vocabulary on the fly. Nation → nación. Reality → realidad. Famous → famoso. Different → diferente. Public → público. Necessary → necesario. The conversion works around 85% of the time at the everyday-vocabulary level and well over 90% in academic registers.

This page is the word-formation engine behind that fact. It covers the seven systematic suffix swaps, the half-dozen spelling adjustments that go with them, and the predictable shifts in stress and pronunciation that the spelling rules don't tell you about. A companion page, Cognados verdaderos, covers the same territory from the vocabulary side; this page is about the rules.

Why the rules work

Both languages took a Latin word and adjusted its ending to fit native phonology. Latin natio, nationis became English nation and Spanish nación by two different routes from the same source. The patterns concentrate in suffixes because endings carry grammatical information and were the most regular part of Latin. Memorise the suffix swaps and 70% of the work is done.

The seven core suffix swaps

-tion → -ción (and -sion → -sión)

The single highest-volume cognate pattern. Every English -tion and -sion noun has a Spanish twin in -ción or -sión. All are feminine. All carry a written accent on the ó.

Pattern: nation → nación, station → estación (note: English st- becomes Spanish est-), attention → atención, action → acción, function → función, decision → decisión, conversion → conversión, conversation → conversación, education → educación, conclusion → conclusión.

-ty (and -ity) → -dad / -tad

The second-highest-volume pattern. All -dad / -tad nouns are feminine.

Pattern: city → ciudad, society → sociedad, university → universidad, possibility → posibilidad, identity → identidad, reality → realidad, quality → calidad, quantity → cantidad, security → seguridad, opportunity → oportunidad, responsibility → responsabilidad, liberty → libertad, difficulty → dificultad, faculty → facultad. The -tad variant appears with a small fixed set of Latinate stems (liberty, difficulty, faculty, virtue → libertad, dificultad, facultad, virtud); the more productive ending is -dad.

-ous → -oso / -osa

The classic adjective pattern. Spanish -oso/-osa agrees in gender.

Pattern: famous → famoso, dangerous → peligroso, generous → generoso, religious → religioso, curious → curioso, nervous → nervioso, mysterious → misterioso, delicious → delicioso, precious → precioso, fabulous → fabuloso, ambitious → ambicioso.

-ent / -ant → -ente / -ante

Adjective and noun pattern, mostly invariant in gender (one form for both): un estudiante / una estudiante.

Pattern: important → importante, different → diferente, evident → evidente, present → presente, intelligent → inteligente, dependent → dependiente, urgent → urgente, frequent → frecuente, abundant → abundante, elegant → elegante, brilliant → brillante, tolerant → tolerante. Watch the consonant clusters: frequent loses the u (frecuente), and intelligent simplifies the double l (inteligente).

-al → -al (no change)

The simplest pattern: write the English word and adjust pronunciation. Spanish -al adjectives are invariant in gender.

Pattern: cultural, personal, central, national, international, social, natural, professional, original, normal, formal, mental, animal, legal, criminal, fundamental, total, vital, hospital, capital — all identical in spelling.

-ic / -ical → -ico / -ica

Adjective pattern with mandatory written accent on the antepenultimate syllable. Spanish keeps the suffix tight at -ico where English often expands to -ical.

Pattern: classical → clásico, electrical → eléctrico, political → político, economic → económico, automatic → automático, fantastic → fantástico, public → público, basic → básico, dramatic → dramático, romantic → romántico, historical → histórico, practical → práctico, logical → lógico, magnetic → magnético. The accent is not optional — writing publico (without accent) makes it the verb form "I publish".

-ary → -ario / -aria

Adjective and noun pattern with gender agreement.

Pattern: vocabulary → vocabulario, dictionary → diccionario, ordinary → ordinario, contrary → contrario, necessary → necesario, voluntary → voluntario, primary → primario, secondary → secundario, salary → salario, anniversary → aniversario.

Spelling shifts that ride alongside the suffix swaps

The suffix rules tell you most of the story. The remaining mismatch lives in the stem, and a small set of spelling rules covers most of it.

ph → f

English keeps the Greek ph in scientific vocabulary; Spanish has always written it f.

Pattern: philosophy → filosofía, photo → foto, phase → fase, phenomenon → fenómeno, telephone → teléfono, photograph → fotografía, alphabet → alfabeto, elephant → elefante, physics → física, geography → geografía.

th → t

English keeps the Greek th; Spanish writes t.

Pattern: theatre → teatro, theme → tema, theory → teoría, theology → teología, thermometer → termómetro, athlete → atleta, mathematics → matemáticas, sympathy → simpatía, method → método, theme → tema.

Double consonants collapse to single

Spanish nearly always reduces English double consonants to single. The exceptions are the two letters that genuinely have a different sound when doubled: rr (a trilled flap, distinct from single r) and ll (in peninsular yeísmo, the same sound as y; historically distinct).

Pattern: professor → profesor, common → común, possible → posible, traffic → tráfico, official → oficial, occasion → ocasión, immediate → inmediato (with mm → m), attention → atención, accommodate → acomodar, recommend → recomendar.

k → c / qu

Spanish does not use k in native vocabulary (it appears only in loanwords like kilo, karate, kiwi). The Latin k-sound is written c before a, o, u, l, r (casa, color, cura, clase) and qu before e, i (queso, quince). Pattern: chemistry → química, quantity → cantidad, queue → cola (etymology differs but the pattern is visible), Christ → Cristo.

-ssion → -sión

English -ssion drops a -s- in Spanish: commission → comisión, profession → profesión, expression → expresión, mission → misión.

The pronunciation traps

You can write a cognate correctly and still pronounce it badly. Three traps catch English speakers.

Stress shift

English and Spanish stress words very differently. Hospital in English: HOS-pital. In Spanish: hos-pi-TAL. Animal: English AN-imal, Spanish a-ni-MAL. Universal: English u-ni-VER-sal, Spanish u-ni-ver-SAL.

The Spanish rule: words ending in a vowel, n, or s stress the penultimate (second-to-last) syllable; words ending in any other consonant stress the final syllable. Words that violate the rule carry a written accent showing where the stress actually falls.

The peninsular /θ/ for c+e/i and z

In peninsular Spanish (with the exception of much of Andalusia and the Canaries), c before e/i and z are pronounced as /θ/, like English th in thin. So gracias /ˈɡɾaθjas/, nación /naˈθjon/, plaza /ˈplaθa/, cinco /ˈθinko/. Peninsular Spanish distinguishes casa /kasa/ from caza /kaθa/; Latin American and southern peninsular do not.

Pure short vowels

English has twelve vowel sounds; Spanish has five (a, e, i, o, u), all pure and never reduced. Importante is /im.poɾ.ˈtan.te/ — every vowel clean, no schwa.

Common Mistakes

Key Takeaways

• The seven suffix swaps convert thousands of English words into Spanish words on the fly: -tion → -ción, -ty/-ity → -dad/-idad, -ous → -oso, -ent/-ant → -ente/-ante, -al → -al, -ic/-ical → -ico, -ary → -ario.
• All -ción, -sión, -dad, -tad, and -tud nouns are feminine. All -ción / -sión nouns carry the written accent. All -ico nouns and adjectives carry the written accent on the antepenultimate syllable.
• The spelling adjustments: ph → f, th → t, double consonants collapse to single (professor → profesor, commission → comisión), and st- at the start of an English word becomes est- (station → estación).
• The strategy is about 85% reliable. The other 15% breaks into false friends (embarazada, librería, sensible, éxito), register-shifted cognates (adquirir is more formal in Spanish than acquire is in English), and gender-irregular Greek-origin nouns (el problema, el tema, el sistema, despite the -a ending).
• The pronunciation traps are stress shift, /θ/ for c+e/i and z in peninsular Spanish, and pure short vowels with no reduction.
• Cognate density rises with register. A grocery list is mostly Anglo-Saxon-vs-Romance-native and has few cognates; a newspaper article is half cognate. Read the higher-register text when you want your English vocabulary to do the most work.