The philosopher who is generally considered to be the person who coined the term "blank slate" (Latin, tabula rasa) is John Locke. He believed that when we are born, our brains are like slates (a small chalkboard used by students in his time) on which nothing has yet been written. Every experience we have in life "writes" itself onto that slate. His philosophical stance is called empiricism, or the belief in the reliance on the senses for understanding the world around us.
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The idea come from Platon, or maybe others presoctratics. The idea exactly of `blank slate´. But the new founder in the modern age come from Locke. In the age happened a big controverse between the racionalism thinkers and empiriscism thinkers, more less, the empiricism thinkers come from the Britain islands, and the racionalism thinkers from the continent.
After the idea was taked for politicals ideologies, since XIX to now the empiricism is a tipical idea of the left people (marxism and others), and the racionalism to the rigth people (nacism and others).