Brøndal received a traditional education in philology but showed an early concern for theoretical problems.
This background made him receptive to the ideas of the prestructuralists (such as Antoine Meillet) during his studies in Paris (1912–1913).
He read Ferdinand de Saussure's Cours de linguistique générale immediately after its publication as he was proofreading the final version of his sociologically oriented thesis on language history (Substrater og Laan i Romansk og Germansk, 1917).
His ultimate purpose was to find the basic features of language that maintained it as an intentional phenomenon in the phenomenological sense used by Franz Brentano and Husserl.
The requirements of structural linguistics helped Brøndal to define the categories in necessary and sufficient interrelationship for morphological and syntactical purposes.
Every element of language is integrated in the grammatical structure on a qualitative and a quantitative basis: qualitatively, it is defined by the double dichotomy of morphology versus syntax and symbol versus logic; quantitatively or formally, it is defined by the structural principles for differences and similarities between elements.
In Ordklasserne, Brøndal tries to characterize the specificity of a given totality (the morphology of a language) from the presence and absence of its constituents (the word classes).
Later, Brøndal improved his analysis of structural regularities in generalizing them to include all parts and levels of grammar.
When developing the principle of symmetry, Brøndal sets up six forms of relation, which indicate the formal possibilities of the manifestations of a given element: positive, negative, neutral, complex, positive‐complex, and negative‐complex.
On this basis, they create a link between the qualitative and the formal characteristics of the grammatical units: if, in a given language, a grammatical element (e.g., a word class) is formally defined as complex, then the internal differentiation of the class will be more restricted than the internal differentiation of an element of less complex definition (positive, negative, or neutral).