All these classifications, and others, are important in linguistics, the study of language. As these examples show, linguists can classify languages according to their history, as well as according to the language's structure and according to how words are formed. Here are three common classifications that linguists use and how Spanish fits in with them:
Genetic classification: The genetic classification of languages is closely related to etymology, the study of the origins of words. Most of the world's languages can be divided into about a dozen major families (depending on what is considered major) based on their origins. Spanish, like English, is part of the Indo-European family of languages, which includes the languages spoken by around half the world's population. It includes most of the past and current languages of Europe (the Basque language being a major exception) as well as the traditional languages of Iran, Afghanistan and the northern part of the Indian subcontinent. Some of the most common Indo-European languages today include French, German, Hindi, Bengali, Swedish, Russian, Italian, Persian, Kurdish and Serbo-Croatian.
Among Indo-European languages, Spanish can be further classified as a Romance language, meaning that it is descended from Latin. Other major Romance languages include French, Portuguese and Italian, all of which have strong similarities in vocabulary and grammar.
Typological classification by basic word order: One common way of classifying languages is by the order of the basic sentence components, namely the subject, object and verb. In this regard, Spanish can be thought of as a flexible subject-verb-object or SVO language, as is English. A simple sentence will typically follow that order, as in this example: Juanita lee el libro, where Juanita is the subject, lee (reads) is the verb and el libro (the book) is the object of the verb.
It should be noted, however, that this structure is far from the only one possible, so Spanish can't be thought of as a strict SVO language. In Spanish, it is often possible to leave out the subject entirely if it can be understood from the context, and it also is common to change the word order to emphasize a different part of the sentence.
Also, when pronouns are used as objects, the SOV order (subject-object-verb) is the norm in Spanish: Juanita lo lee. (Juanita reads it.)
Typological classification by word formation: In general, languages can be classified as isolating or analytical, meaning that words or word roots don't change based on how they are used in a sentence, and that the relationship of words to each other are conveyed primarily by the use of word order or by words known as "particles" to indicate the relationship among them; as inflectional or fusional, meaning that the forms of the words themselves change to indicate how they relate to the other words in a sentence; and as agglutinating or agglutinative, meaning that words are frequently formed by combining various combinations of "morphemes," wordlike units with distinct meanings.
Spanish is generally viewed as an inflectional language, although all three typologies exist to some extent. English is more isolating than Spanish, although English too has inflectional aspects.
In Spanish, verbs are nearly always inflected, a process known as conjugation. In particular, each verb has a "root" (such as habl-, to which various endings are attached to indicate who is performing the action and the time period in which it occurs. Thus, hablé and hablaron both have the same root, with the endings used to provide more information. By themselves, the verb endings have no meaning.
Spanish also uses inflection for adjectives to indicate both number and gender.
As an example of the isolating aspect of Spanish, most nouns are inflected only to indicate whether they are plural or singular. In contrast, in some languages, such as Russian, a noun can be inflected to indicate, for example, that it is a direct object rather than a subject. Even names of people can be inflected. In Spanish, however, word order and prepositions are typically used to indicate the function of a noun in a sentence. In a sentence such as "Pedro ama a Adriana" (Pedro loves Adriana), the preposition a is used to indicate which person is the subject and which is the object. (In the English sentence, word order is used to inidicate who loves whom.)
An example of an agglutinative aspect of Spanish (and of English) can be seen in its use of various prefixes and suffixes. For example, the difference between hacer (to do) and deshacer (to undo) is in its use of the morpheme (a unit of meaning) des-.
Online references: Ethnologue, "Classification Scheme for the Languages of the World," "Linguistics: The Study of Language" by Jennifer Wagner, "Indo-European and the Indo-Europeans" by Calvert Watkins.