Hilaritas (elation or cheerfulness), for Spinoza, is a joy that expresses a perfect affective equilibrium of the body's parts (and, indeed, of all the parts of our being), which are identically or equally affected with this affect. He promptly adds in Ethics IV, 44 Schol., however, that hilaritas ‘is more easily conceived of than observed’. Yet Spinoza also endeavours to convince us that:

• 1. While this joyful affect, indeed, only occurs very rarely or fleetingly in practice, it is an adequate expression of the necessary structure of all existence insofar as it is wrapped up in the essential love for oneself and/or the conatus itself, which it develops and affirms in a certain proportion of motion-and-rest.

• 2. Hilaritas points to a direct, practical and affective path (of balanced joy) for the formation of adequate ideas. This is the way to our freedom, since it implies a dynamic passage from passive to active affects.

• 3. Therefore, hilaritas is also, and above all, the adequate expression of the necessary ethical existence par excellence, namely, of acquiescentia in se ipso. Acquiescentia finds its origin in reason, and the essential equilibrium this ‘contentment’ implies is, by Ethics IV, 52 Schol., ‘the highest good we can hope for’. As per Ethics IV App. 4, it is also ‘the ultimate end of the man who is led by reason, i.e., his highest Desire, by which he strives to moderate all the others, is that by which he is led to conceive adequately both himself and all things that can fall under his understanding’.

• 4. Lastly, found at the very heart of Ethics IV, hilaritas announces that the ethical end is, as much as possible, acquiescentia in se ipso. It is the complete agreement of a human being with herself, equally and positively affected in all the parts of her body and mind.

To address the question of the structural underpinnings of reason and human freedom, therefore, we shall follow the dynamism and vital balance that hilaritas assumes and expresses in Ethics IV. Even if experience shows us how rare this vital balance is, reason and Spinozist philosophy nevertheless presuppose its necessary and immanent presence in any activity, especially in the practice of ethics.