Barba non facit philosophum

W.'s reading a book of Latin philosophical phrases. – 'Ah, here's something that applies to you: Barba non facit philosophum. A beard does not make a philosopher'. What does eo ipso mean? What's the difference between modus tollens and modus ponens? – 'Tabula rasa: I know you know that. And conatus – even you must know that'.