 In his commentary on the Categories, Marsilius adheres to William of Ockham’s and John Buridan’s view that the ten Aristotelian categories are distinguished by the way they refer to things in extra-mental reality. The emphasis here is on the ‘way they refer to’ things, i.e., their modus significandi, and not on the things themselves, he argues, since distinct categories like ‘quantity’ and ‘quality’, while doing so in different manners, may still refer to one and the same individual thing in the outside world, e.g., Socrates. Different categories, therefore, do not represent different things but stand for distinct and unique ways of signifying  things.[7]  Together, the ten categories cover all possible ways of speaking about things. Like Buridan, however, Marsilius emphasizes that it is impossible to prove that their precise number is and must be ten, as some philosophers like Albert the Great had claimed. It is only lengthy experience that has led philosophers to acknowledge their number to be  ten.[8]  If an additional mode of signifying things was discovered in the future, Marsilius states, he would readily accept there to be more than ten Aristotelian categories, even though he does not consider such a discovery to be very  likely.[9] 