Modernity simply refers to a modern time period (1500 to the present) -- one that is post-agrarian and characterized by capitalism, rationalism and the nation state. Modernity is the modern era of humanity to the degree that such a rapidly evolving notion can be categorized. Modernism, a more nuanced social and cultural movement spanning approximately 1890 to 1939, operates within modernity, but is a distinct entity. All told, there are several important differences between the two that you must understand to draw a division between the closely related concepts.

Context

Modernity exists in a post-industrial context. It is everything that can generally be seen as modern, and therefore exists as a historical period informed by all those before it. It stands as an era of social relations most commonly associated with capitalism and a new global awareness. This new order is where modernity differs from modernism. Modernism as an artistic and cultural movement operated within the context of the rejection of this realism and rejection of the development of concrete values.

History

Modernity was born out of an agriculture-based society in which representative democracy was far from the norm. The tumultuous socio-political events of the prior few centuries were the birthing pains of this new era -- an era at odds with what came before it. Modernism's development was more subtle. It manifested itself historically through art and cultural expression. It rejected the conservative values of the past, through the likes of philosopher Theodor Adorno, and embraced the concept of self-consciousness.

Influence

Modernity is the newest chapter of history, and yet has been influenced by the past in such a way as to drive itself away from the past ways of life. Therefore, you might consider the political and economic changes in national governance, the development of North America, and economically crushing wars -- such as the Napoleonic wars -- as factors that soured modern opinion toward the past's aging norms. Modernism is more influenced by culture and social changes, including a turning away from Enlightenment thinking and the weakening influence of the church.

Direction

Modernity as a historical period is not likely to progress much further. Post-modernity is a term that has been used by academics, as early as Nietzsche, to describe a contemporary society that is a somewhat separate entity than that of the industrial revolution. Similarly, modernism is not expected to retain a dominant position among artists, yet it will likely live on for a time as postmodernists decipher the movement -- interpreting the ways in which it will be remembered and the ways in which it continues to influence emerging art forms.