21.2.2 Synthetic form of the comparative / superlative bom, mau
We speak about synthetical formation if the grammatical function is expressed by a change of the word itself. John's book for example is a synthetical formation, the book of John is a analytical formation. The comparative of good is formed in a synthetical way, better, and the comparative of beautiful in an analytical way, more beautiful.
For historical reasons some adjectives / adverbes forms the comparative in a synthetical way and others in an analytical way.
synthetical formation of the superlative
good - better
bad - worse
big - bigger
small - smaller
* remark: mayor in Spanish means older, but not bigger. The comparative of grande in Spanish is más grande. The analytical form mais grande in Portuguese is almost always wrong. It can be used only if two qualities of the same object are compared.
mais grande if two qualities of the same object are compared
Nosso apartamento é mais grande do que confortável.
Our appartmente is rather big than comfortable.
One should see that in this case we don't compare two object with respect to one quality but one object with respect to two qualities.
** Same logic as with mayor. In Spanish the meaning of menor is younger, mi hermano menor <=> my younger brother. In Portuguese however menor means small.
Beside that the construction is the same as described in 21.2. Instead of the analytical form mais + adjective the synthetical form is used.
comparative with synthetical form
A casa do João é maior que a do Paulo.
The house of João is bigger than the house of Paulo.
O castelo é o maior de todos.
The castle is the biggest of all.
Meu apetite é maior do que o do meu irmão.
My appetite is bigger than the one of my brother.
O remédio é pior que a doença.
The medicine is worse than the sickness.
The corresponding adverb to mau is mal. However the comparative is the same for the adjective and the adverbe: pior.
The corresponding adverb to bom is bem. However the comparative is the same for the adjective and the adverbe: melhor.
The adverb and the adjective have therefore the same comparative.
comparative of mal, bem
Este casaco fica-te bem, mas aquele fica-te melhor.
This jackets fits you well, but that jackets fits you even better.