The AL Rule (Major)

This Rule applies to those words in English with two or more syllables that end with the letters

To translate them into Spanish, we will substitute the ending with

(simple enough?)

English words ending in ....sial or ....tial that sound like "S" are translated to Spanish by using the ending ....cial.
In Spanish, when "c" precedes an "i", it is pronounced like an "s" (see Quirk # 8).
As an example, the English word partial is the Spanish word parcial.
The English word Hortensial is the Spanish word Hortensial.
Otherwise, the spelling will be the same (observing the quirks).
English words ending in ...tial in which the "t" sounds like " t" (as in bestial), are spelled the same in Spanish (bestial), so here are a lot more Examples

The AL Rule

English Spanish Helpful Reminders
Abdominal Abdominal
Aboriginal Aboriginal
Accessorial Accesorial only 1 S, quirk #8
Accidental Accidental
Actuarial Actuarial
Administerial Administerial
Alluvial Aluvial only 1 L
Ambisexual Ambisexual
Angelical Angelical
Annual Anual only 1 N
Antisocial Antisocial
Antiviral Antiviral
Arboreal Arboreal
Arterial Arterial
Asexual Asexual
Astral Astral
Aural Aural
Axial Axial
Bacterial Bacterial
Baronial Baronial
Basal Basal
Bestial Bestial
Bilateral Bilateral
Bifocal Bifocal
Binocular Binocular
Bipolar Bipolar
Bisexual Bisexual
Brutal Brutal
Capital Capital
Carnal Carnal
Casual Casual
Caudal Caudal
Celestial Celestial also Celeste
Central Central
Centrifugal Centrifugal
Cereal Cereal
Cerebral Cerebral
Cervical Cervical
Coaxial Coaxial
Cogenial Cogenial
Colonial Colonial
Colossal Colosal only 1 S
Commercial Comercial only 1 M
Communal Comunal only 1 M
Continental Continental
Cordial Cordial
Corporal Corporal
Corpuscular Corpuscular
Coradial Coradial
Corral Corral
Cortical Cortical
Cranial Cranial
Credential Credencial C for t
Criminal Criminal
Crystal Cristal I for Y
Crucial Crucial
Cultural Cultural
Decimal Decimal
Dental Dental
Dextral Dextral
Diagonal Diagonal
Dictatorial Dictatorial
Differential Diferencial only 1 F, C for T
Digital Digital
Dimensional Dimensional
Distal Distal
Dominical Dominical
Duodecimal Duodecimal
Duodenal Duodenal
Electoral Electoral
Elemental Elemental
Epidural Epidural
Equatorial Ecuatorial C for Q
Equilateral Equilateral
Essential Esencial only 1 S, C for T
Eternal Eternal also Eterno
Evangelical Evangelical
Extralegal Extralegal
Extramarital Extramarital
Extramural Extramural
Facial Facial
Fatal Fatal
Federal Federal
Festival Festival
Filial Filial
Final Final
Focal Focal
Formal Formal
Fraternal Fraternal
Frontal Frontal
Fundamental Fundamental
Funeral Funeral
Galaxial Galaxial also Galáctico
Genial Genial G pron. like H, quirk #12
Genital Genital G pron. like H, quirk #12
Gradual Gradual
Harmonial Harmonial quirk #1
Hexagonal Hexagonal
Hibernal Hibernal quirk #1
Homosexual Homosexual quirk #1
Horizontal Horizontal quirk #1
Hospital Hospital quirk #1
Ideal Ideal
Illegal Ilegal only 1 L
Immoral Inmoral N for M
Imperial Imperial
Impersonal Impersonal
Inaugural Inaugural
Incidental Incidental
Individual Individual
Infernal Infernal
Initial Inicial C for T
Integral Integral
Intellectual Intelectual only 1 L
International Internacional C for T
Jovial Jovial quirk #2
Judicial Judicial quirk #2
Labial Labial
Lacrimal Lagrimal G for C
Lacteal Lacteal also Láctea
Lateral Lateral
Latitudinal Latitudinal
Legal Legal
Liberal Liberal
Lineal Lineal
Literal Literal
Litoral Litoral
Local Local
Longitudinal Longitudinal
Madrigal Madrigal
Magisterial Magisterial
Manual Manual
Menial Menial
Marginal Marginal
Marsupial Marsupial also Marsupio
Marital Marital
Martial Marcial C for T
Maternal Maternal also Materno
Medieval Medieval
Menstrual Menstrual
Mental Mental
Meridional Meridional
Mezcal Mezcal
Metal Metal
Mineral Mineral
Mistral Mistral
Mitral Mitral
Modal Modal
Monaural Monaural
Montreal Montreal
Monumental Monumental
Moral Moral
Mortal Mortal
Mural Mural
Musical Musical
Narial Narial
Nasal Nasal
Natal Natal
National National
Natural Natural
Naval Naval
Nepal Nepal
Neural Neural
Neutral Neutral
Nominal Nominal
Normal Normal
Nutritial Nutricial C for T, quirk #8
Occidental Occidental quirk #8
Occipital Occipital quirk #8
Official Oficial only 1 F
Oral Oral
Orbital Orbital
Orchestral Orquestral QUE for CHE
Oriental Oriental
Parental Pariental note "I"
Parietal Parietal
Palatial Palacial C for T
Pastoral Pastoral
Paternal Paternal also Paterno
Pectoral Pectoral
Pedal Pedal
Pedestal Pedestal
Penal Penal
Pentagonal Pentagonal
Perinatal Perinatal
Personal Personal
Plural Plural
Portal Portal
Primordial Primordial
Principal Principal
Proverbial Proverbial
Provincial Provincial
Proximal Proximal
Punctual Puntual no "C"
Quintal Quintal
Rabbinical Rabinical only 1 B
Racial Racial quirk #8
Recital Recital
Regional Regional
Renal Renal
Residencial Residencial
Residual Residual also Residuo
Rival Rival
Rural Rural
Sacerdotal Sacerdotal
Sectorial Sectorial
Semental Semental
Semifinal Semifinal
Semiformal Semiformal
Sensual Sensual
Sensational Sensacional C for T
Sentimental Sentimental
Serial Serial
Sexual Sexual
Sisal Sisal
Skeletal Esqueletal quirk #6 & #7
Social Social
Spatial Espacial quirk #6, C for T
Special Especial quirk #6
Spinal Espinal quirk #6
Sequential Secuencial C for Q, C for T
Structural Estructural quirk #6
Subliminal Subliminal
Tangential Tangencial C for T
Temperamental Temperamental
Tempestual Tempestual
Temporal Temporal
Terminal Terminal
Testamental Testamental
Tetragonal Tetragonal
Textual Textual
Thermal Termal no "H"
Timbal Timbal also Tímbalo
Topical Topical
Torrential Torrencial C for T
Total Total
Tribunal Tribunal
Tropical Tropical
Umbilical Umbilical
Uncial Uncial quirk #8
Unilateral Unilateral
Universal Universal
Urticarial Urticarial
Usual Usual
Vaginal Vaginal
Venal Venal
Venial Venial
Verbal Verbal
Vertebral Vertebral
Vertical Vertical
Vestigial Vestigial G pron. like H
Vial Vial
Viral Viral
Virginal Virginal
Visual Visual
Vocal Vocal

There are many, many more! They might look like English words, but they are also Spanish! You can double up on what you have just learned, too:
For the plural on the Spanish words above, just add!
The plural for Universal, for example, is Universales!
Proper pronunciación of the Spanish vowels is everything!
We can forego the practice session, yes?
Who said you couldn't learn Español?

A few exceptions to this Rule, are:

English Spanish Helpful Reminders
Continual Continuo
Magical Mágico
Petal Pétalo
Terrestial Terrestre

There are possibly many more "exceptions" to the Rules than are put forth in the examples. Those that are listed are the ones which are most common. Remember, however, that the Major Rules, on a percentage basis, have very few exceptions and the overwhelming odds are that you will correctly translate English words to Spanish by applying the Rules. In most cases, even the exceptions are similar enough to be understood by a Spanish-speaking individual, so you should feel confident that, when you are speaking the words, you are making yourself understood!