Paul Erdős's father, Lajos Erdős, who taught mathematics in Budapest, had taught himself English during the First World War while held captive in Siberia from 1914 to 1920, but he badly mispronounced many words. When he taught his son English, he passed these mispronunciations on to him, and Paul Erdős retained them for the rest of his life.
To him, people who did no mathematics were trivial beings (trivial being). For his own part, he did mathematics constantly: some of his friends spoke of him devoting nineteen hours a day to it. Everywhere and at all times, even when he was not alone, he was absorbed in thought. When he felt ready to do mathematics with others, he would say that his brain was open (my brain is open). Thinking, posing problems and trying to solve them were the sole purposes of his life.
At the age of 58, after the death of his mother, with whom he had an exceptionally close relationship, he suffered from depression and was prescribed psychotropic medication. He remained dependent on such drugs for the rest of his life. He nevertheless managed to stop taking them for a time, but the effect on his mathematical creativity was too severe, and he resumed the medication to recover his ability to think.
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Erdős had a habit of using certain expressions with his friends and coauthors, almost certainly with a great deal of humor; they knew how to decode them.
