The classification of word classes is a central topic in grammatical research on Modern Turkish. Identifying and clarifying the functions of words within sentences is an essential criterion for determining word types. Semantic, formal, and syntagmatic features are used in the word categorizing process. In the grammar sources of Modern Turkish, researchers typically classifies word types based on various criteria. In addition, to explain the usage of a word in different classes, it is important to explore whether words are confined to specific categories or whether transitions between word classes can occur. To determine a word’s type, its function in the sentence must be considered. A word can shift to a different class without structural changes. This phenomenon is called a "functional shift." In Modern Turkish, such shifts are observed between some nouns, adjectives, and adverbs.

The distinction between word types is emphasized in grammatical research. Identifying word types helps to clarify their functions in a sentence. For example, words in the subject position of a sentence must typically be nouns, whereas words that describe or qualify nouns are usually adjectives. Establishing the word type is a critical step in understanding the roles of words within a sentence. At this point, it is useful to define the terms "word" and "word type." A word is a unit comprising one or more sounds that performs a syntactic function and carries meaning within a sentence. Word types are groups of words that share common grammatical features and can function interchangeably within syntax. The semantic, formal, and syntactic features are considered when classifying word types.

This study aims to demonstrate functional shifts between word classes. In this context, four pairs of antonyms that can function as nouns, adjectives, and adverbs in Modern Turkish were selected based on their relatively high frequency in the Türkçe Ulusal Derlemi / Turkish National Corpus (TUD/TNC): güzel (beautiful) - çirkin (ugly), yakın (near) - uzak (far), sıcak (hot) - soğuk (cold), yanlış (wrong) - doğru (correct). These words were selected because they can function as nouns, adjectives, and adverbs without any suffixation or changes in form. Sample sentences illustrating the usage of these words as nouns, adjectives, and adverbs were extracted from the TNC.

In the first section of the study, the perspectives of researchers who have worked on classifying words in Modern Turkish were examined. In this regard, two main approaches to the classification of word types in Modern Turkish can be identified. The first approach groups words into three categories: nouns, verbs, and prepositional origins. In this classification, nouns, pronouns, adjectives, and adverbs are categorized as "noun words," verbs form a separate group, and prepositions, conjunctions, and interjections are grouped as "prepositional words." In contrast, the second approach divides word types into eight categories: nouns, adjectives, determiners, pronouns, prepositions, conjunctions, exclamations, and verbs. Based on this, it can be concluded that there is no consensus on the classification of word types in the literature.

The second section of this study focuses on the functional shifts between nouns, adjectives, and adverbs. Based on the opinions and explanations provided in grammatical sources, it is evident that nouns, adjectives, and adverbs classified as nominal in Modern Turkish can undergo class shifts within sentences. These shifts occur without structural changes to the words. For a class shift to occur in a sentence, semantic and syntactic compatibility is required.

In the third section, the functional shifts explained in the previous section are demonstrated through a database of sentences. The study sample comprises 120 sentences containing five randomly selected examples in which the specified words are used as nouns, adjectives, and adverbs. The syntagmatic relationships between nouns, adjectives, and adverbs were analyzed within these sentences, and usage patterns were investigated. Each sentence was coded based on the word's function as a noun, adjective, or adverb. The placement of words within sentences and syntactic elements before and after them were also analyzed, and a formula representing word order in the sentences was developed.

In the evaluation section, these formulas were classified according to their usage as nouns, adjectives, or adverbs. The formulas were then compiled into a single formula and explained in tables.

In the conclusion section, based on the analysis of the selected sample sentences, formulas regarding the word order required for a word to function as a noun, adjective, or adverb in a sentence were provided. It was concluded that words classified as nominal in Modern Turkish (nouns, adjectives, and adverbs) can be explained using a syntactic formula and form a pattern. Increasing the number of words and sentences in future research and verifying the accuracy of these formulas will further contribute to the literature.