The existing controversy surrounding the terms Spanish and Spanish is based on what is right or appropriate to refer to the language spoken in Spain, in all Latin America, in Equatorial Guinea, or in other areas with strong presence of Spanish speakers. To try to explain the differences between the two, see the definition given in this respect the Dictionary pan Hispanic:
To designate the common language of Spain and many nations of America, and that is also spoken in other parts of the world, as the English and Spanish terms are valid. The controversy over which of these names is more appropriate today is surpassed. The Spanish term is preferable for lack of ambiguity, since it concerns of unmistakable way the language spoken today about four hundred million people. It is also the name that is used internationally (Spanish, anglais, English, Spanish, etc.).
Still also being synonymous with Spanish, it is preferable to reserve the term Castellano to refer to the Roman dialect born in the Kingdom of Castile during the middle ages, or the dialect of Spanish spoken in this region currently. In Spain, the Spanish name is also used when it refers to the common language of the State in relation to the other co-official languages in their respective autonomous, such as Catalan, Galician or the Basque territories.
Use of the terms Spanish and Castilian
There are people who use the term to refer to the language as opposed to foreign, languages and relationship to other languages which are also Spanish in Spain. This is recommended by Manuel Seco in his dictionary of doubts and difficulties of Castilian.
However, as you can see in the picture, there are countries in Latin America that prefer the use of Spanish against the Spanish.
What the Constitution say Spanish regarding the terms Spanish and Castilian?
The Spanish Constitution of 1978 established Spanish as the official language of Spain, to differentiate it from the other official Spanish languages. According to article 3.1 of the Spanish Constitution, "the Castilian is the official Spanish language of the State"; Likewise, article 3.2 States that «the other Spanish languages will also be official in the respective autonomous communities in accordance with their statutes".
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However, according to the SAR, this use which is made of the Castilian term does not exclude the use of the Spanish that is recommended.
Latin American constitutions
In the constitutions of Latin American countries, the Spanish/Spanish terms are used depending on the country.