Using like as a conjunction is ranked as #7 in a list on onlinecollege.org of the 20 most controversial rules in the grammar world. In Traditional grammar and usage, like is used as a preposition, while as is used as a conjunction.
However, the online Cambridge Dictionary asserts that like and as can function as both prepositions and conjunctions.
When used as prepositions, they have different meanings. Consider the comparisons below that the site provides.
As + a noun means
“in the role of”
As your father, I’ll help you as much
as I can.
The speaker is the listener’s father.
Like + a noun means
“similar to” or
“in the same way as”
Like your father, I’ll help you as much as I can.
The speaker is not the father but wishes to act in a similar way to the father.
When used as conjunctions, as and like have the same meaning, but using like as a conjunction is considered more informal, which The New Fowler’s Modern English Usage states as the “coded language of modern grammarians” for “illiterate,” “vulgar,” “sloppy” (458).
For instance, the style book of the British journal The Economist states that “like governs nouns and pronouns, not verbs and clauses. . . . as in America not like in America, as I was saying, not like I was saying” (89).
As with other controversial grammar rules and myths, you as a writer have the choice to decide the usage based on your own preferences, your audience, and the context. If you’re writing for an academic or a professional setting, you would probably do best to follow the traditional rule to avoid notice or censure of people like the modern grammarians mentioned above; if you’re writing for more informal or “jocular” or creative situations, then using like as a conjunction should not cause debate.
(Most of the content of this essay is adapted from The New Fowler’s Modern English Usage. Additional material came from dictionary.cambridge.org, ecugrammar.blogspot.com, and mentalfloss.com. For a fuller discussion of the topic, refer to the longer post, “Using like as a conjunction.” See the interview with Cronkite on YouTube where he discusses his handling of the Winston ad slogan. The Winston “ungrammatical” ad controversy continued into the 70s when the company produced another advertisement, playing off the academic reaction to the 1950s slogan by showing the slogan being discussed in an English class, which resulted in a clever op-ed accessed here.)