Many anthropologists, linguists, psychologists, biologists and other academics have attempted to tackle this question in recent decades. It is sort of "chicken or egg" conundrum: Did human beings first develop the physical capabilities for language (larger brains, vocal tract, etc) with the actual development of language following it, or had the capabilities for speech already arisen and only with the development of physical production of language itself follow?
Obviously, it is difficult for us to think about things without using "language" in our minds while we reason. Yet if you've ever had a smart pet and watched them perform a task, you know that they operate on a largely trial-and-error basis.
Semantics is the study of the meaning of language. This is a sub-discipline of linguistics that breaks down the meanings of words into logical notation, similar to the language of math. It may be that in a few centuries we can accurately break down the brain functions, how they operate together at thousandths of a second to combine the various logical meanings in our head and eventually produce well-formed sentences and sounds that have value and meaning to other speakers of language.
The question “Can we think without language” is a difficult one - one that requires even more questions from philosophers - how do we "know" anything (epistemology). At a basic level - yes we can think without language insofar as animals clearly can do it. However, language allows us to organize information in a particularly expressive and powerful way which has allowed human civilization to flower and technology to proceed in the manner it has.
The current worldviews that human beings possess are obviously products of the long cultural, educational, and biological tradition we have inherited. For example, we may not see in infrared vision, or many of the various wavelengths of the whole spectrum, nor do we hear certain Hz of the waves...