With más + adjective + que it is indicated that a quality appears to a greater degree: Ana es más alta que Luis. With menos + adjective + que the opposite is indicated: Este libro es menos interesante que el otro. The structure compares two people, things, or ideas and makes clear which has more or less of that quality. To form these ideas, the adjective keeps its basic form, just like in Adjetivos Descriptivos, and only the words that mark the comparison change.

To say that two things have the same quality you use tan + adjective + como: Mi casa es tan grande como la tuya. The first element presents the quality and como introduces the second term of the comparison. This form appears frequently when comparing size, speed, price, strength, or beauty: El café está tan caliente como antes. Against differences in comparisons, here you do not express superiority or inferiority, but equality.

When talking about quality, result, or value in daily life, the regular comparative is not always used. Mejor and peor replace más bueno and más malo in natural comparison: Esta mesa es mejor que la anterior, Hoy me siento peor que ayer. Más bueno only sounds normal in very literal uses or contexts where you compare amount of goodness, not quality. With food, service, movies, or work, the usual choice is to select mejor or peor. That same choice appears alongside Adjetivos Cuantitativos when the contrast depends on quantity and not on quality.

Mayor and menor do not function only as general comparatives. They are used for age: Mi hermana es mayor que yo; for size or extent: La casa mayor del barrio; and for importance or rank: Un problema mayor. Menor marks the opposite value: lower age, smaller size, or lesser relevance. In some contexts, mayor and menor express a more precise difference than más grande or más pequeño, especially in formal registers and in common expressions like de mayor a menor.

There are comparisons in which que is obligatory because it links the two terms. It occurs with forms such as mejor que, peor que, mayor que, menor que, más de and menos de when a quantity is compared to a number: Tengo más de diez libros, Llegó menos de una hora tarde. It also appears in expressions like antes que and después de que, where the comparison or sequence relation is fixed by the structure. In these cases, the word that changes the content is the comparative, not the link.

Some comparatives change to agree with the noun or the subject, and others stay fixed. Mayor and menor agree when they come before a noun: las ciudades mayores, los problemas menores. By contrast, mejor and peor usually function as fixed forms when describing quality: la opción mejor, el servicio peor. After Concordancia Adjetival, it is useful to observe whether the word behaves as an adjective that accompanies the noun or as a stable comparative form that does not change.

The choice depends on what is being compared. If the idea is quantity or intensity, usually más, menos or tan appear: más rápido, menos caro, tan fuerte como. If the comparison affects quality, result, or value, mejor and peor usually appear: Este plan es mejor que el otro. If talking about age, size, or rank, mayor and menor typically come in: el hermano mayor, una empresa menor. The position of the adjective can also change the nuance, as seen in Posición del adjetivo, but the key remains what exact relationship between the compared elements you want to express.