Therefore, if we could say of past philosophy that it has been an attempt to understand the world and man's place and destiny in it—an attempt necessarily conditioned by the class outlook, prejudices and illusions of the various exploiting class philosophers—we have to say of Marxist philosophy that it is an attempt to understand the world in order to change the world and to shape and realise man's destiny in it. Dialectical materialism is a theoretical instrument in the hands of the people for use in changing the world. Marxism, therefore, seeks to base our ideas of things on nothing but the actual investigation of them, arising from and tested by experience and practice. It does not invent a "system" as previous philosophies have done, and then try to make everything fit into it.
from Materialism and the Dialectical Method - Maurice Cornforth
In the context, what did the author mean by "them"? "ideas of things" or just "things"?